When car is cold and deaccelerating I hear a rattling like it's coming from the muffler. Will do it on steady throttle but not as noticeable. When the car is warmed up you can't hear it at all. Anyone have this issue. Would catalytic converter be the culprit if someone ran a tank of regular through it? Thanks.

 

Not just the exhaust "burble"? I find the burble/popping more noticeable when the engine is cold.

Check this http://motoringfile.com/2005/06/28/exhaust_popping/

..and many other threads.

e.g. https://www.northamericanmotoring.co...ad.php?t=60126

 

Sounds like an exhaust pipe rattle. The reason it dosen't do it when it's hot is that the exhaust pipe has expanded and stretch enought to tighten up what ever it is thats loose enough to rattle when cold. I would check all exhaust pipe mounts, mainly the one just under the shifter. That's usually the culprit.

Let us know

 

Teeth? (I couldn't resist!)

...Les

 

I have the same thing going on (exhaust rattle when the engine is cold). It's ok after warmup.
I have been all over the underside of the car and can find no loose mounts or shielding but did notice that if I put my foot on the tailpipe to stop the vibration it stops rattling.
It almost sounds as though it's coming from "inside" the exhaust.
This came about after the OBX header install and I am wondering if by not having the flex joint in the header it is causing more vibration downstream.

 

Thanks for all your replies. I'm taking it to my friendly mechanic for a look see. Will post result.