Rattle/Clunk under vehicle while driving.

[Proxa]

99 Tahoe z71
5.7

While in park and throttling - no rattle

While slow coasting over bumps - no rattle

While gently accelerating at or above 10MPH - slight rattle

When gears shift - rattle starts and then reverberates slightly


I cant figure out where to start. The transmission seems strong, only a rough shift from 1st to 2nd from which I understand to be normal for the 4l60-e. I checked the U joints by pulling on them and they are nice and snug. Any help pointing me in the right direction would be appreciated.

 

[mikk999]

maybe something in the exhaust like the converter or muffler. does it sound like something rattling ?

 

[Proxa]

Yes, it sounds like a rattle. I shook the exhaust and could not reproduce the sound. If it was the exhaust; would it would make that sound while in park and throttling?

 

[lesterl]

Internal baffle in the muffler, might bang on it with a rubber mallet in a few spots to crease the case slightly and see if the problem is temporarily cured.....

 

[Proxa]

I just did some research on baffle noise, just so happens that flowmasters are notorious for failed baffle welds. I will try his first thing in the AM. I just don't understand why I wouldn't be able to reproduce the sound while not moving.

 

[Proxa]

Well, I hit the mufflers with a rubber mallet and didn't hear anything that resembled the sound I am talking about. I did the same thing with the cat, and it looks like that may be the problem. Any way to make sure before I start throwing money at it?

 

[MO Viet Vet]

Possible crack at the flex plate? Something loose in front of engine? Heat shield?

 

[nharkey85]

Im thinking a heatshield as well. Sometimes the beating/shaking doesnt create the correct motion to replicate the rattle. Different RPM and load on system works the same way

 

[lesterl]

You get a sympathetic vibration that will rattle heat shields and baffles, take an old coat hangar (metal) and take it apart, wrap around the cat you suspect and twist it pretty tight (dont crush the cat or snap the hangar, just some extra pressure), then test drive for the noise......

 

[Proxa]

Looks like you guys were right. After beating the crap out of everything with a rubber mallet , the sound is gone. It's probably temporary until I can inspect further, but I can at least rule out serious repairs. I'll revisit this post when I finally track down the culprit, which is looking like one or maybe both cats.

 

[Deebo]

Transfer Case

I would say your transfer case is messing up. Mine rattled for a while until the chain from it finally beat it's way out if the case. I bought and new used one but it was from a 98 Tahoe and mine is a 99. Now my tahoe will not up shift out of first and the speedo reads 0 all the time. I read that it could be my VSS and I went a checked and I have 4 or 5 plugs for the transfer case that are not plugged in because they do not fit. Do you guys think I could cut the existing wires as rewire them with new plugs that do fit the transfer case? Should I just buy a new case or should I try to find plugs to put in the case that fit my wire harness? Reverse also doesn't not work.

 

[Proxa]

LOL, you just Deebo'd my post.