Chevy Tahoe, Cold-start rattle in exhaust

Alright Chevy guys, lets see if you have any ideas for this one... Now that it has gotten cold in the mornings our 2010 Tahoe 5.3L occasionally makes one hell of a rattle when first started. It sounds like it is coming from the converters, but by the time I can get crawled under it the noise has pretty much stopped. When I pull out on the road and accelerate, it also makes a rattle noise for a few seconds...but after that, you can drive it all day without a sound.

All of the heat shields are tight, and I can't find anything loose. Whatever it is only happens on a cold start, once everything is at operating temperature there is no noise.

I have had the material inside a converter break up before, but that rattled all the time...I'm stumped on this one.

Yeah, my first guess would have been the heat sheilds. They came loose on every car we have owned.

Second guess is the catalytic converter. I had a 2004 Silverado that had the comb inside break and it rattled all around. Warranty job if new enough.

kevin

You mean that has been check and replaced and it still rattles?? Hmmmm

Just had that problem with the girl friends ( that's right, this old grump has a girl friend) newish Subaru--definetly converter heat shield--hers didn't seem loose either--I took a long walking stick &, from the top, pushed down on the converter shield & that was it--right where the pipe goes into the converter in the rear==I know this is Freetownish--but I took an axe handle steel wedge & ball peened it between the pipe & converter shield--I know--real rustic, but it worked---stop over thinkin it & give it a try

There are no heat shields around the converters themselves, just around the manifolds and above the converters on the floorpan. I have pulled and tapped on all of them, and also the converters...still can't replicate it. I read online that the oxygen sensors can rattle...but I won't go that far until I have tried the Freetown wedge & mallet method.

Nothing you can't fix with a ballpeen hammer!!

Kevin

KLook wrote:Nothing you can't fix with a ballpeen hammer!!

Kevin

My favorite tool.... the BFH

Try searching.....gm knocking noise when cold....on the net.
Alot of 5.3L GM motors do this. My 1999 Silverado does.
Glynn

I am familiar with the piston slap of engines from that period, this is something totally different.

Get used to it Rob. It's "today's" Chevrolet. My Silverado makes more noises than my '94 K1500 did with 266,000 miles on the clock. What pisses me off the most about it is I could've bought 10 K1500's for what I paid for this thing.

But anyway ...sounds like it's definitely exhaust related. It's the only place where things expand enough to stop a rattle, besides inside the engine. Mine has noisy lifters & piston slap when cold too.

This morning I eliminated the manifold heat shields as a cause, and determined that the noise is down in the transmission area. This morning it almost seemed like it could be the torque converter, but the cat. converters are right near it so who knows. I will keep trying to narrow it down, but it is tough to diagnose when the noise doesn't last long.

I know I'm showing my age---BUT--do you have a dust shield to get up at the TC---I know I had that problem on the old (78) plow truck & could spin the fly wheel & tighten the VERY loose TC--remember---kids at BOCES rebuilt this whole thing--they kinda did good, but weren't real good at tightening bolts LOL Intake manifold bolts were finger tight double LOL---friggin kids triple LOL

10-4 on the TC shield, didn't find anything loose there. What I need to do is park it on ramps the night before, that way I can quickly get under it after a cold-start. Maybe I will get lucky and something will really start making a racket...easier to diagnose that way.

Haven't had time to get back under it, but here is a short video of the "rattle", easiest to hear towards the end.

http://youtu.be/pp6XsIOsL0o

Ya checked your flywheel ring??? I know you were in there --BUT-- I'd check that back & forth/ side to side. Unfortunatly if it's not there, it sounds real internal. That's automatic, yes???