God Awful Muffler Rattle

[TeamGomez]

So on cold starts I all of a sudden got an annoying as hell (read: loud) rattle coming from the left muffler. I haven’t racked it yet to pinpoint exactly where its coming from, but I would swear that it sounds like one of the valves is chattering…except it isn’t. I got behind it when it was rattling and stuck a long screwdriver in the inboard tip up against the valve and no joy. Visual inspection of valve closed shows zero chatter.

From the side, it sounds as if the rattle is coming from the front end of the muffler just aft of the intake port. Hertz matches vibration frequency as though there’s a ratchet sitting on top of the muffler. Rattle is the same with muffler valve open or closed and will diminish after muffler heats up.

I can’t find any similar issues on a search with a rattle at the front of the muffler that would lead me to any solution before racking it and pinpointing the exact location with said long screwdriver to my ear as I hunt for the exact lat/longs. Thinking new muffler at this point; hope I’m wrong.

TIA-

~John

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[OLD8BA]

my neighbour had rattle in his muffler on his 2020 GT we put it up on stands i got under while he started it
i ended up using a rubber mallet and gave it a whack where the noise seemed to be coming from it put a dimple in muffler and stopped the rattle
rough but its been good for about 2 yrs now
i did same many yrs ago on my Tmodel {v8} new smitthy muffler rattled fixed that too

 

[TonyNJ]

I've dealt with this before. Two things...


Check the rear hanger bracket. Two bolts into the body. The nuts are welded into the frame and I had one snap off. Had to put a rivnut in there as a replacement.

But it's prob, the welds that hold all the hangers onto the muffler pipes. I've also had one of those crack. Specifically the one by the rear differential. It's hard to even see unless you get it on a lift and remove the rear plastic pan. Then you have to really get in there and push on the exhaust to see the crack open, or start it with eyes on it.

Here's a Pic of where mine cracked. It would make a really bad noise on start up and while revving, not not at idle. I re-welded it and it was all good.

 

[TeamGomez]

Thanks a ton @TonyNJ and @OLD8BA. Gonna go put it up in the air and see what I can figure out. Snapped weld sounds like a winner… I will return with diag.

 

[TeamGomez]

Well, that didn’t take long. Put her up on the 4 post and located rattle with a rubber mallet. Looks like the same place as your second pic @TonyNJ. This is a brace tube about as thin as a Coors can that connects left and right exhausts just fwd of the rear sway bar at the hanger. This is looking fwd just right of centerline thru rear tray.

I just bent it up about an eighth for the near term.

Welding Coors cans together above my pay grade. May just leave it but guessing it’ll find the next weak point and break there. Got a buddy who can knock it out.

Thanks again for the help.

Looking aft and you can see the tubing that connects l/r side. Crack is behind hanger on left side of the pic.

 

[OLD8BA]

excellent glad all is well again cheers Dave

 

[TonyNJ]

Yup. That's exactly where mine broke. I think it happened from the exhaust bottoming out on a steep driveway exit over a crest. Heard it scrape. Days later heard the noise.

FYI, before I welded mine, I temporarily jammed a piece of rubber heat resistant tubing between the crack to stop the noise. Worked like a charm until the weld repair.

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