I did search the exhaust rattle threads. They all seem to deal with bad mufflers (baffles broken loose), bad resonators or bad cats. None really seemed to touch on exhaust rattles that only happen when the car is cold.

Mine just started doing this tonight. It's obnoxious and kind of embarrasing. It only happens when I first start the car and goes away after I rip through the gears a couple of times; once everything has warmed up.

I have a custom 2.5" stainless axleback with a Borla turbo muffler, done by a local speed shop. Would like to avoid taking it to the dealer and getting hassled about it. If it's the resonator, fine with me. I was going to replace it with a Magnaflow eventually anyways.

Anyone have any ideas, keeping in mind it goes away once the system warms up? Again, it's a rattle, sounds like something is loose. Checked the rear hanger, seems fine. Nothing seems loose. New system from the axle back was fully welded, not sure what there are for stock clamps never looked that close. Do the noisy (problematic) stock resonators shut up after they warm up?

 

And this morning the sound was gone. Focken strange.

 

I still have the stock exhaust on my car, but I'm getting the EXACT same problem. Noise at start up, but as soon as it all warms up, its fine. I'm taking it to the dealer tomorrow to get it and a few other minor things looked at, I'll let you know what they say.

I'm just guessing but, I think its the CAT. Except for the fact that the noise goes away, the noise its making is the same noise as when I had a bat CAT on my sunfire.

 

Thanks for the reply. The sound has come back a couple of times now. It's doing this about once or twice a day. Very intermittent, and by the time I work through the gears once after a cold start, it's gone. Please let me know how you make out, and good luck.

 

Got the car back, the noise my exhaust was making (and going away after it heated up), was from the Resonator (sp?). They were out of the part in stock, so I have to go in early next week when my replacement comes in.

Tell them to check it when you go in. Hope that helps.

 

Hmmm... I have a $15 customer credit sitting on my account at Summit Racing. I might just order a Magnaflow and get it put in before winter. Thanks for the update, I'm glad they fixed your problem. Let me know if it comes back!

 

The rattle is starting to happen a bit more frequently now, seemed to happen every time I fired up my car yesterday as well as this morning. I took a stab in the dark and ordered a new resonator this morning from Summit, since I was going to install a new one anyways. I hope this does the trick

 

Mine rattles a bit when I hit 2500rpm in 1st and 2nd gear from a cold start

 

Had my Magnaflow resonator installed on Monday. And well... the problem wasn't my stock resonator. It was actually my aftermarket tip. I have a stainless steel double wall exhaust tip on my aftermarket axleback, and that's where the noise was coming from. Apparently the welds had broken so the two walls were rattling together at the end of the tip. They tack welded it in a couple of spots and now there's no noise. The tack welds don't look the best though, so when I get the rest of my exhast done next year I might ask for a TIG bead all the way around that inner edge to give it a finished look. This is exactly why I didn't want to go to the dealer to get them to check it out, just in case it was a problem with my mods. Which it was

At any rate, the Magnaflow resonator has really cleaned up my exhaust sound and didn't cost much to install, and I was going to do it anyways. So it's all good

 

Reproduce the sound at your dealership and they will give you a new one. Thats what I did. Got a whole new muffler. Thanks GM!

 

Forgot to repost after I got it fixed, they ended up replacing my entire exhaust. Either way, sounds much better and no weird start up noise.