Rattling noise sounds like heat shield.

KShi · March 25, 2021

Hi everyone,

I'm new to this forum, I have a 2019 GMC Sierra SLT. I'm having trouble figuring out where the metal clinging noise is coming from under my truck. The sound only happens when the truck is warm and driving at a constant speed. It will not rattle when I'm accelerating or decelerating etc. I'm having trouble getting it to rattle parked in the driveway and this is why it's difficult to figure out. I checked all the heat shields and they seem to be pretty secure with the dealership saying the same thing. I've also looked around to see if I have any clinging marks anywhere to no avail. I've gone over the mileage for the bumper to bumper warranty and the dealership wants to charge me to figure it out. Has anyone had this same issue or similar experiences and figured out the problem?

Therickyp · March 26, 2021

My truck did the same thing when i first got it and it was the shield around the spare tire. Its easy to bend.

eppieguy · March 28, 2021

There also have been some reports of the internal muffler rattling, mine is doing it, just waiting for another reason to,go to the dealer to get it replaced.

AJMBLAZER · March 28, 2021

Check your exhaust flapper(s).

My wife’s Yukon was doing something similar. Was the flapper valve in front of the muffler.

Removed it. No more noise.

KShi · April 8, 2021

@eppieguy yes, tapping on my muffler it seems to be coming from the inside of it. Have you had this checked out yet? Do you know if its covered under warranty? 2019 GMC sierra with 48k miles. Not sure what warranty this would be classified under but maybe bumper to bumper, which I wouldn't qualify because my miles.

eppieguy · April 8, 2021

No, I have not had it checked out but I saw a post from another member and it was warrantied for him. I am waiting until I need something else fixed before I bother with it, my warranty expires in December and I have 30k on it so if nothing else crops up between now and then I'll take it in December. It's really not bothering me so right now I don't really care and if I can find a GM performance exhaust before then I won't even take it back.

KShi · April 13, 2021

Thanks everyone, It was the baffles inside the muffler as I suspected from tapping on the muffler. Going to do an aftermarket exhaust (bolt on) as they quoted me $1,350 to have the muffler replaced which is crazy. I am over miles on bumper to bumper and my Ally major guard extended warranty apparently doesn't cover the costs. Hope this helps someone.

AJMBLAZER · April 13, 2021

Any good exhaust shop would put the 3 inch muffler of your choice under your truck for a couple hundred bucks tops.

David T Harrington · July 9, 2021

Just had the same rattle issue. 2019 GMC Sierra 1500 SLT Crew Cab Short Bed with 16,500 miles.

Only happens when it's hot. Sounds like a heat shield is loose. Especially noticeable with the rear slide window open.

It's an internal baffle in the muffler that has come loose. Part number for my repair was 84657793 which is the muffler, pipe and brackets. The part list price is over $800.00.

Mine got worse over time, mine would do it really bad at medium speed, about 45 mph.

To prove it while stationery, get it good and warm and tap the muffler with a rubber mallet.

Mine was covered under factory 36 month / 36,000 mile warranty.