Very odd clunk/thud while in park?

[Opeth]

Ok, so this has me stumped and occurs in an even odder time.

I'll start the truck up cold and drive 3-4 miles down the road no issues and park at the store. Walk around the store maybe 10 mins, come back out and start the truck. I'm not putting the truck in gear just sitting in place. About 20-30 seconds later, a loud thunk or clunk occurs from the front passenger side. It's severe enough to feel it through my seat, and it's quite startling. I don't know where it's coming from, whether in the dash or outside the vehicle in the drive line.

I first thought it was my 4 wheel drive, but I cycled from 2hi to 4 hi and everything worked normally, all usual sounds.

Any suggestions where to start. It's happened a few times now, but not consistent.

 

[Matt]

This is just a wild guess...but isn't the secondary air injection thing in that area? And the 20-30 seconds timing sounds right for that too.

 

[The_Roadie]

SAIS turbine pump is under the driver's seat, and sounds like a shop vac. The SAIS check valve is on the exhaust manifold, and if the hoses were messed up it could allow exhaust noises to escape for those 20-30 seconds. Definitely need to open the hood and listen around when the noise happens.

 

[Opeth]

Pretty sure it's not the air injection, that starts and whirls as usual. This is coming from the passenger front side of the vehicle somewhere. It feels like something is slamming shut in the HVAC system( vent door maybe), or something was bound up and releasing the tension off itself. It's violent enough to where I can feel the clunk/thud through the body of the truck, which is why I thought maybe the disco was acting up and somehow was disengaging. It's just one quick thud/clunk.

I have noticed it only has happened when the vent selector is on defrost mode, with the HVAC turned off this clunk has not occurred. My dash vents stopped blowing air back in May but haven't gotten a chance to fix that yet, and also there is a hissing sound from tHe A/c dryer area after the truck was shut off which I think is probably normal, prolly dripping on the exhaust mani.

I'll see if I can get it to do it tonight on the way to work, but pop the hood and jump back out after I start the truck and listen from the passenger side.

 

[Opeth]

Ok, figured out where the thud is coming from. The a/c dryer near the passenger side fire wall. I'm not sure why this is occurring, but the dryer is popping up in its black holder within the washer fluid reservoir. My a/c system functions just fine, the dryer is ice cold as normal. Going to see if it's not fully seated in its holder or the stupid dealership neglected to re-install it properly after my head install. They didn't re-install numerous connectors on the wire harness back to their original spots, and I am missing a couple bolts from the PCM mounting bracket..... Soo.... I wouldn't be shocked.


How do you switch this to a solved issue? I can't edit my first post anymore.

 

[Menthol]

Pretty sure it's not the air injection, that starts and whirls as usual. This is coming from the passenger front side of the vehicle somewhere. It feels like something is slamming shut in the HVAC system( vent door maybe), or something was bound up and releasing the tension off itself. It's violent enough to where I can feel the clunk/thud through the body of the truck, which is why I thought maybe the disco was acting up and somehow was disengaging. It's just one quick thud/clunk.

I have noticed it only has happened when the vent selector is on defrost mode, with the HVAC turned off this clunk has not occurred. My dash vents stopped blowing air back in May but haven't gotten a chance to fix that yet, and also there is a hissing sound from tHe A/c dryer area after the truck was shut off which I think is probably normal, prolly dripping on the exhaust mani.

I'll see if I can get it to do it tonight on the way to work, but pop the hood and jump back out after I start the truck and listen from the passenger side.

Can someone please let me know if the above bolded comment is a normal AC operating sound?

Thanks.
Vince

 

[Wooluf1952]

I've heard that sound on my Envoy. IMHO, it's not unusual.

 

[Menthol]

I've heard that sound on my Envoy. IMHO, it's not unusual.

Thanks.