Trailblazer Rattling Noise

[RTTBLT1]

Hello everyone.

So the TB started making this horrible rattling noise underneath the vehicle the other day. Sounds like bolts bouncing around or popcorn popping. I have only heard this noise in Park at Idle and it does not do it all the time. Also doesn't do it on short trips, after 15-20+ miles of driving it then it will do it. Below is a Video of this sound...

So far I have checked most of the large-medium bolts underneath the vehicle from the Transfer Case to the front bumper and have not found a fault. Also checked all the Exhaust, Engine, Gas Tank Shields/Plates and all appear to be tight with no play/slop. And I took off the access cover for the Transmission to check the Torque Converter and doesn't seem to be coming from that particular location and the Torque Converter is spinning true.

In person and to me it sounds as if it's coming from the Exhaust system or the Transmission. Next time it does this, I plan to take a 3/8 or 1/2 in Extension to the Exhaust components and place it to my ear to see if I can find the culprit.

Additional info:
Current miles 171,900
Engine & Trans appear to be original/factory
Exhaust systems appear to be original/factory (except Resonator delete Pipe)
No current CEL light and Engine Trans runs & shifts great.

So what do you guys think/suggest?...if anyone has experienced this sound/issue please let me know.

Thanks in advance!

 

[AWD V8]

That noise is the guts of the CAT rattling loose inside. When the CAT is cool, take the palm of you hand and hit the bottom of the CAT, you will hear it rattle then.

If it gets bad enough, the pieces inside will turn sideways and clog the outlet and you will have a great lose in power. Fix it now.

 

[RTTBLT1]

That noise is the guts of the CAT rattling loose inside. When the CAT is cool, take the palm of you hand and hit the bottom of the CAT, you will hear it rattle then.



If it gets bad enough, the pieces inside will turn sideways and clog the outlet and you will have a great lose in power. Fix it now.

I was thinking Exhaust component as well.

I went out and hit the CAT pretty good a few times and didn't hear anything out of the ordinary. So I also tried hitting the Muffler and same thing, nothing out of the ordinary.

Still thinking it's either the CAT or the Muffler.

 

[JimInRadfordVA]

Sounds like a cat on the way out. Hit the bolts with PB Blaster every day for a few days before you try to unbolt it. Good luck and let us know what happens.

 

[Mooseman]

Maybe grab the exhaust with a heavy or welder's glove. You might be able to feel it.

 

[AWD V8]

It may be "just" on the way out. When it's hot the shell expands and the gut float around. When it's cool the shell shrinks and holds the guts tight so it won't rattle.

^^ use a welders glove and try hitting it again when it's hot and making noise.

Still confident it's the CAT.

 

[DocBrown]

Sounds like a cat on the way out. Hit the bolts with PB Blaster every day for a few days before you try to unbolt it. Good luck and let us know what happens.

And even that may may not be enough. I had to heat the bolts up with an oxy/acetylene torch.

 

[Sparky]

I'm assuming you checked the big heat shield above the muffler as well. Mine rotted around the nuts that hold it up and it was sitting on top of the muffler making noise. It wasn't a metallic rattle noise because that shield isn't just a piece of metal, it was more dull sounding. I used some large fender washers to hold it back up and that did the trick for about 5 years.

Cat is definitely suspect though.

 

[RTTBLT1]

Maybe grab the exhaust with a heavy or welder's glove. You might be able to feel it.

It may be "just" on the way out. When it's hot the shell expands and the gut float around. When it's cool the shell shrinks and holds the guts tight so it won't rattle.

^^ use a welders glove and try hitting it again when it's hot and making noise.

Still confident it's the CAT.

Ok, i will have to give the welders glove tip a try not time it's acting up. I will keep this thread updated.

I'm assuming you checked the big heat shield above the muffler as well. Mine rotted around the nuts that hold it up and it was sitting on top of the muffler making noise. It wasn't a metallic rattle noise because that shield isn't just a piece of metal, it was more dull sounding. I used some large fender washers to hold it back up and that did the trick for about 5 years.

Cat is definitely suspect though.

Yes sir I did, I checked all the Exhaust Heat Shields and was unable to find a fault.


If I end up having to replace the CAT...I'm debating on purchasing the CAT, Muffler, Flanges and Both 02 Sensors through Rockauto and having a local well known Exhaust Shop install it all (expect the 02 Sensors). Based on the horror stories I've heard about removing Exhaust Bolts.

I will keep this thread updated. Thanks everyone!

 

[Sparky]

AC or Denso for the O2 sensors only (pretty sure Denso makes the AC Delco ones anyway). I had a Bosch in mine which surprisingly was OK but GMs have a reputation of not caring much for Bosch stuff.

I found an OEM brand new old stock muffler on ebay a few years ago for relatively cheap when my entire exhaust rotted off the truck. Don't let anyone tell you it is stainless, it isn't. Or, if it is, my truck still managed to rust it out It was easily one of the most expensive repairs I had ever done to the thing as literally everything was shot past the heads, and 8 or 9 of the bolts broke off in the head and they had to extract them

 

[RTTBLT1]

AC or Denso for the O2 sensors only (pretty sure Denso makes the AC Delco ones anyway). I had a Bosch in mine which surprisingly was OK but GMs have a reputation of not caring much for Bosch stuff.

I found an OEM brand new old stock muffler on ebay a few years ago for relatively cheap when my entire exhaust rotted off the truck. Don't let anyone tell you it is stainless, it isn't. Or, if it is, my truck still managed to rust it out It was easily one of the most expensive repairs I had ever done to the thing as literally everything was shot past the heads, and 8 or 9 of the bolts broke off in the head and they had to extract them

Oh ya, plan to go AC Delco on the O2 Sensors. Not to familiar with Bosch but one thing I will say about them is they make a good Alternator. I have a factory/oem Bosch 125 Amp Alternator on my 06 Impala with 276k miles on it and it's still going strong.


I was going to do the Exhaust job myself cause the Bolts doesn't look like they would be difficult to remove but looks can be deceiving...

But I also noticed the Tailpipe is Welded to the rear of the Muffler and since I don't own a Welder figured I would just let a Exhaust Shop do the install...

And I was going to leave the Tailpipe (pipe over rear axle) since it looks to be in pretty good shape...

If the two was not Welded I would probably do the job myself at home.

Also, here is a picture of the CAT. Which doesn't look in too bad of shape/condition...but that's on the outside...

 

[Sparky]

You could just cut the pipe, and then use a clamp like this type to hold the stuff together.

 

[RTTBLT1]

You could just cut the pipe, and then use a clamp like this type to hold the stuff together.

I do own a Sawzall. If I end up going this route would I need to purchase a additional Flange Gasket/Seal?...or does that piece have one built-in?

 

[Sparky]

The new cat should have the flange etc. Depending on the muffler you use it may have the mating flange already on it, so the only part you'd need to clamp would be the tail pipe to the muffler.

Is your muffler shot? Maybe just replace the cat with a direct fit replacement and then you can just bolt it up and not cut anything (assuming the bolts come loose).

 

[RTTBLT1]

The new cat should have the flange etc. Depending on the muffler you use it may have the mating flange already on it, so the only part you'd need to clamp would be the tail pipe to the muffler.

Is your muffler shot? Maybe just replace the cat with a direct fit replacement and then you can just bolt it up and not cut anything (assuming the bolts come loose).

The Muffler is rusting, not shot. But figured I would just replace it as well.

For the brand of replacement parts...I see the brand Walker alot for GM Exhaust components. And I was going to purchase this CAT and Muffler from Rockauto...Walker 55477 Ultra Converter...

And this Muffler...Walker 21421 Premium Quite Flow SS...


Is the Walker brand the oem/factory components for the Exhaust system?

 

[DocBrown]

If you are buying your exhaust parts online, make sure to do your research. I just did the exhaust on my Sierra. I bought the muffler and tailpipe from Amazon mostly because I have Prime, and the pipe between the crossover and muffler from Summit Racing. Auto Zone wanted $180 for that pipe, Summit had it for $119 and free shipping, same pipe, same brand (Walker). Everything arrived in just a few days.

And don't feel you have to weld everything. My previous system was welded, I used heavy duty clamps on the new pipes.

 

[Sparky]

Walker doesn't make the OEM stuff, but I guess they're OK.

 

[DocBrown]

Yea, in my experience the Walker parts will not last as long as OEM, but there doesn't seem to be a lot of choices out there. I have not looked at buying GM exhaust parts but I can't imagine they are cheap.

 

[Sparky]

They aren't. That's why I was pumped when I found the new old stock OEM muffler on ebay for cheap.

 

[Mooseman]

From past posts, Walker mufflers have a lower flow/higher backpressure and apparently are necked down from 2.75" to 2.5" inside.
http://gmtnation.com/forums/threads/walker-exhaust.13794/#post-444909
http://gmtnation.com/forums/threads/horrible-mpg-and-weird-idle-drop.11565/page-8#post-431299

2.75" is an oddball size to find, which is why I went to a 3" catback system. Somebody had used a 3" full size truck big block muffler that worked well for him (can't find the post) but would imagine there would be some work to do to make it fit.

 

[DocBrown]

That's interesting Mooseman. My Sierra had a glass pack on it that rusted away. I bought it like that. I replaced it with a Walker stock type muffler. Overall it's smoother and has more power now. I would not have expected that.

 

[Mooseman]

Could be different models of mufflers by Walker. I would certainly look inside to see if it's necked down.

 

[therealsethallen]

I've never liked Walker's products, they just seem really poorly made. Best bet on this would be to find the replacement from a dealer and use that. I think @gmcman said something about the Walker system creating a ton of backpressure.

 

[gmcman]

The Walker Quiet Flow I used was necked down pretty good. There was another member here who used a different Walker setup and was more free flowing, albeit possibly louder than stock.

 

[Mooseman]

Louder is OK

 

[RTTBLT1]

I'm not set on getting the Walker brand, it's just I have seen a lot of GM direct-fit Exhaust components from Walker and assumed that was what GM installed factory/stock.

I may end up keeping the Muffler till it gives signs of needing replaced. I figured I would replace it based on the fact the CAT looks in good shape/condition on the exterior but interior being shot...so I figured what does the interior of the Muffler look like...??? But after looking more closely, it will probably be ok for at least a few more years/miles...here's a few pictures of the current Muffler...what do you guys think?...

Front (to CAT) connection...

Rear (to Tailpipe) connection...

And while underneath I noticed this sticker on the Tailpipe which says Walker...???...


So after reading the replies about Walker and closely looking at the current Muffler, I think I will continue to run/use it.

Few questions...

1. Do you think the Muffler is good for awhile?

2. I know (now) to avoid Walker Mufflers...but are the Walker OEM direct-fit Catalytic Converters ok to use/install without losing MPG, HP, sound ect?

 

[Mooseman]

1. Yeah
2. I would think so. I have an off-brand one and I have zero backpressure

 

[Sparky]

That muffler looks like it has life left.

I went with a Magnaflow high flow direct fit cat on mine... Well, except I ordered the EXT version by accident so they had to shorten the pipe leading to the muffler lol oops.

 

[RTTBLT1]

Ok, since I will be doing the job at home...Would you recommend...

1. Purchasing new Flange Studs/Bolts and Nuts for both ends of the CAT for reinstall?

2. After spraying PB Blaster for a few days...Would I have better chances of removing the Exhaust hardware without breaking/shearing the Studs/Bolts by hand or with a Impact Gun?

I do plan to reinstall everything by hand with a Torque Wrench. And I already have all the Torque specifications for the Exhaust hardware and O2 Sensors thanks (again) to @Mooseman for the posted PDF'S.

 

[Sparky]

If you have an impact go for it. Loosening won't shear stuff any easier than by hand, and it would at least save your arms. Now, tightening stuff with impacts, that's another story...

If you get a new cat it should have the flange hardware with it I believe. I don't recall if the studs are on the cat side of the flange, or the muffler side. Pretty sure on the manifold side the studs are part of that manifold.

 

[RTTBLT1]

I also forgot to ask...would a bad or partially clogged CAT cause...

1. Decline in MPG?...currently getting around 360-380 miles on a full 25 gal tank.

2. Slightly higher than normal Engine Temps while running the A/C?...with outside temps in the 90-100F (heat index of 98-110) range, Engine Temps have been running (at most) 220-230F.

 

[Mooseman]

1. Definitely yes
2. I don't know. It's possible I guess. I'd be checking the cooling system as it should be able to handle whatever heat the engine throws at it. Maybe the fan crapped out. Test it
How to test the electro-viscous fan clutch

 

[RTTBLT1]

1. Definitely yes
2. I don't know. It's possible I guess. I'd be checking the cooling system as it should be able to handle whatever heat the engine throws at it. Maybe the fan crapped out. Test it
How to test the electro-viscous fan clutch

Have tested the Fan Clutch and Water Pump already and both appear to be good. And it also has a new T-Stat, CTS and Coolant.

I was just curious if a bad CAT could be the culprit behind the Temps. Other than Coolant mix possibly being off, I'm not sure what could be causing the slightly higher Temps in hot weather.

 

[Sparky]

Yeah, it could.

 

[RTTBLT1]

Yeah, it could.

Ok, well hopefully after I replace the CAT the Engine Temps will straighten out.

Thanks guys.

 

[RTTBLT1]

Sorry everyone been busy busy...but didn't forget about this thread...

So this morning I had the Catalytic Converter tested...

It is not a Cat issue...tested good!

So now I'm looking into the O2 Sensors. Both the Upstream & Downstream Sensors look to be original/factory...



So my question is: if it was a bad/worn O2 Sensor, wouldn't the CEL be illuminated on the Instrument Panel?

 

[Mooseman]

Not necessarily. It might just be getting lazy. Mine wasn't throwing a code but replaced it anyway, saw a 2 MPG increase.

BTW, if the downstream O2 sensor is not throwing a code, don't bother with it. All it does is report to the PCM that the cat is working. That's all.

 

[cornchip]

Ok....weird that I came to GMTNation looking for fix 'almost' this exact problem.. I have a 2007 and only have a metallic rattle under throttle. I believe in my case it might be the flex joint (outer wire mesh came off in my hand like a Donald Trump's toupee) . Otherwise it has no visible cracks/leaks. Sounds loose inside...but not bad. Any thoughts?

Clint.

 

[Mooseman]

The mesh is decorative more than anything. I ripped mine off, no ill effects.

For the rattling, just hit the COLD exhaust system from end to end with your hand and listen for the noise. Should be able to pinpoint it.

 

[cornchip]

I gave this a try tonight in the driveway. I'd say it's equally as loose inside the flex joint as it is in the first muffler (baffles?). Just not enough to convince me. I need to set up a GoPro and get a recording from below. Stay tuned.