Noise @ 2k RPM

scalawag

Original poster
Member
Mar 28, 2012
17
Just came over from the ghost town as per a PM, too funny. I have an 04' TB with a noise I'm having trouble pinning down. It's sort of a ticking noise that starts at 2,000 RPM until the thing shifts out of the RPM range. It almost sounds like a plastic noise, like a poker card in the spokes of a bicycle, but hard to tell if it's a plastic noise or what. I have to be bringing the engine speed up somewhat rapidly to produce the sound, and if I really punch it the sound is accompanied by a slight vibration. The sound can be heard in park or neutral, but you have to be inside with doors and windows shut, can't hear it outside of vehicle (hence my trouble). I really doubt it's a valvetrain issue, and I have looked up and down and all around the thing a million times over for loose parts that may be flapping around to no avail.

My wife overheated it when the water pump when out a year and a half ago and I replaced the pump with a cheap autozone unit. I use AC Delco parts exclusively, but there were none in town at the time. I had meant to replace it as soon as possible, just haven't done it yet.

Anyways, I'm inclined to think that the problem is the water pump, clutch fan, and/or fan assembly since that is all that changed when the noise started. My plan is to change the water pump to an AC Delco and replace the fan clutch to see if that fixes it. I'm posting in hopes someone has had a similar issue and that my approach is incorrect since I don't want to spend big money on a pump and fan clutch and have it not be the problem. Also, I couldn't get rid of this POS soon enough and I don't want to put anything more into it than is needed, any help would be greatly appreciated!

Side Note: The clutch fan is not binding and despite some slippage with age, is otherwise functioning properly as near as I can tell.

Thanks
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Welcome! You can pull the serpentine belt and run it for a minute without harm. That will tell you if it's a rotating part causing the noise. It may also be a vibrating exhaust manifold or muffler heat shield. Those are tougher to localize.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Hey thanks Roadie, I actually thought of running it without the belt earlier, but unfortunately my wife has the car right now. I'll do it first thing when she gets home. Also, since we're talking talking about belts, do you think it's absurd to imagine that the belt itself could be causing the issue?
I got my hands on all of the heat shields I could find already and they seem to be secure. I took the heat shield off the manifold to see if I could visually see anything, but could find nothing. I read in a thread about a recall on exhaust manifolds, do you know anything about this? Is it still available to have checked out? The problem seems backward from a manifold crack since it gets worse at temp., but I suppose it's worth a deeper investigation.
 

Mypetropig

Member
Dec 29, 2011
226
I had a similar issue a few years back. I removed the belt and determined it wasn't a rotating part issue. After much searching I found that it was the rubber hood bumpers that needed to be adjusted. I ran them out a turn or two and haven't had a problem since. :twocents:
 

scalawag

Original poster
Member
Mar 28, 2012
17
That's interesting about the rubber bump stops, amazing what big problems little things can create. I took the belt off and the noise went away. When I get some time next week I'll throw a new belt on and see if that's the problem, I kind of doubt it though. I'm wondering if the noise is the bearings on the outs with the fan clutch. It will be interesting though, I don't can't seem to find anything wrong with the other accessories to make me think they are a problem.
 

Mypetropig

Member
Dec 29, 2011
226
Stranger things have happened. If the belt doesn't do anything for the noise, the idler pulley and belt tensioner are two fairly cheap parts to throw at it. Hopefully it wont come to throwing money at it. As for parts that have bearings I am sure you know water pump, alternator, a/c compressor and power steering. Good luck! My money is on the cheap water pump.
 

vangasman

Member
Dec 8, 2011
4
The belt on my wifes suburban makes a ticking noise where the splice is every revolution. I got used to it.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Yeah i hope it's just the water pump since i want to replace it anyway. The belt went out a couple weeks before I put the cheap water pump on, and to compound the problem I was too cheap to replace the new belt after it got antifreeze all over it, lol. So I'm hoping a little that maybe that has created the noise, we'll see anyway.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Thanks fire06, you know the more i think about it the more i realize that it's not just about me fixing the noise. I really want to isolate the problem and know exactly what is making this particular noise—maybe help someone out down the line if they have a similar noise. If the belt doesn't fix it I'll be wanting to replace the fan clutch and water pump anyway, so I'll just slap a new fan clutch on and try it, then do the water pump.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Okay, so I figured out the problem a while back and forgot to come here and tell about it. Anyways, It ended up being the hood prop banging against the front/top part of the fan shroud. The more I looked into it, I realized I wasn't hearing the noise in park or neutral, just some grinding noise from the idler and tensioner pulleys which I confirmed with a stethoscope.
So for the full report on symptoms and correction: Rapid tapping noise when driving under light load starting around 2,000 RPM until trans shifts to the next gear. Can't be replicated with car in park or neutral, must be driving. Noise goes away when serpantine belt is off. I don't know if all trailblazers/envoys have the hood prop resting against the fan shroud, but mine was and even left a little rust colored streak where it was touching and rubbed a little groove in the plastic. I temporarily jammed some rags in between the fan shroud and hood prop and went for a drive to confirm that it was the noise and it was, then I got a piece of round foam with the center hollowed out and slid it over the rod for the hood prop at the point it contacts the shroud and good to go.

Thanks to everyone who helped me out. :wootwoot:
 

MacMan

Member
Mar 3, 2012
194
the roadie said:
Appreciate the report.

Hood props are quaint. Outdated, but quaint.

It's all about the weight & gas mileage today. Gas pistons weigh quite a bit more.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Yeah, had a rough time working on the hood prop without a hood prop holding the hood up. lol
 

MacMan

Member
Mar 3, 2012
194
scalawag said:
....working on the hood prop without a hood prop holding the hood up

Yep. Now, say that 3 times real fast.....:biggrin:
 

pennywise

Member
Mar 28, 2012
46
I've had the same problem since buying the truck a few months ago. After reading this thread I went out and bent the prop rod a little to give it more clearance. I haven't done a test drive yet but I will figure out if it worked in the morning.
 

Sparky

Member
Dec 4, 2011
12,927
Interesting! I have a similar unknown rattle at 2500-2800 RPM or so that I could never figure out. I did notice the mark on the fan shroud. Hah, I'll bet it is the same thing.

With the pending efan conversion I guess I'll find out for sure when I rip that shroud out of there.
 

scalawag

Original poster
Member
Mar 28, 2012
17
pennywise, I tried to bend mine and the sound came back. I thought I had it out of the way enough, but apperently not. I was afraid I'd rip it off trying to get good enough clearence so I just rigged up the foam deal. Just saying if it doesn't get rid of the sound jam some old rags in there to make sure that's the problem. I hope that's all it is for you also. Mine looks kind of bad right now, but good enough until I can do what roadie mentioned and get the hood struts.

sparky- I bet it's the problem too. Kind of weird a hood prop tapping against the fan shroud would make you think the transmission is gonna jump through the floorboards.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Okay, so I went out there and got serious about it. I took the dumb thing off and put a pretty gnarly bend in it and it works like a champ. I've got about an inch of clearance from the shroud.
 

pennywise

Member
Mar 28, 2012
46
Bending the rod seems to have worked so far. I only drove it around here on post yesterday, but it wasn't rattling, so hopefully it's good. If not the next suspect would be somewhere in the timing chain. That's what I originally thought it was. Now I have noticed another noise coming from the passenger side rear of the engine. It only happens from 1900-2000 or so RPMs. Sounds like a beer can rolling down the driveway. I'm pretty sure it's a loose heat shield or something along that line. I don't know if it's a new sound or if I just couldn't hear it over the other noise. If I figure it out I will post it here.
 

Sparky

Member
Dec 4, 2011
12,927
Could be the dumb resonator. Others have commented that it rusts inside.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Good to hear, it must have gotten it. Unless we weren't talking about the same noise. The hood prop noise is pretty distinctly coming from the front half of the TB. I could never tell if the noise was the engine, transmission, or dash for certain, but I never thought somewhere in the rear. Like sparky said, the resonator is definitely suspect. I'd look into just deleting it completely. Cheap to do and there are some benifits to it as well from what I understand, plus it may stop the noise.
 

scalawag

Original poster
Member
Mar 28, 2012
17
Somehow I missed where you were worried about a timing chain noise when I read through your post. Just wanted to add that when my rattle went away, I also heard odd things that it was covering up. I broke out the stethoscope again and scoured all over the engine. Everything from idler pulley to listening through the valve cover. Didn't find anything amiss but some slight growl from my pulley bearings that is probably on par with their age, and nothing too alarming. You might try a stethoscope and see if you can track both noises down. If you don't already have one, they're on sale at harbor freight for around $3 right now.
 

pennywise

Member
Mar 28, 2012
46
The initial noise sounded like you described. Rapid tapping under light load. I thought that was the timing chain or valve train. On pushrod engines thats a tell tell sign of its time to upgrade the cam and timing gear. Bending the prop rod worked. I will look into the other noise later. It's raining today here in New Mexico, which never happens. Just poking around yesterday it seems like a heat shield. They are missing nuts in some places. I would like to take the res off, but I don't know when that's going to happen.
 

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