Strange noise after new OEM converter installed

dang5001 · Post by **dang5001** » 08 Apr 2010, 04:37

99 S70 AWD I'm not sure how to explain this, but..... I had a new catalytic converter installed two weeks ago. Now, when I come to stop, the car runs smooth, then there is a gradual increase in a strange, loud noise (like a bad muffler) and the car runs a little rough. The noise gets progressively louder the longer you sit with the car in drive. However, if I put the car in neutral, it idles smooth and when I accelerate from the stop, the noise goes away. When I come to a stop it happens all over, again. The car runs fine otherwise, no CEL's, great gas mileage. Any Ideas or suggestions will be greatly appreciated.

Post by **Ozark Lee** » 08 Apr 2010, 18:33

It could be that the rubber mounts that suspend the rest of the system got strained during the cat / down-pipe replacement process and the muffler or tail pipe is touching something. If you can observe the problem in your drive way you can use some heavy gloves to move the rear portion of the exhaust system around to narrow the problem area down. The exhaust system grows as it heats up and things that seem clear when cold can actually rattle once things heat up.

...Lee

Post by **jblackburn** » 08 Apr 2010, 22:48

Grab the heat shield & try to shake it around. I had a muffler replaced once, and it rattled something awful every time I decelerated, turned out they didn't tighten down the heat shield.

dang5001 · Post by **dang5001** » 09 Apr 2010, 04:28

Thanks for the advice. I'm taking it back to the shop that installed the cat, today. When I called him yesterday, the first thing he said was he thought the motor mounts might be bad. However, I didn't have this problem before the new cat was installed. I'll post back later whn I find out something.

dang5001 · Post by **dang5001** » 09 Apr 2010, 08:01

Ended up being the right front motor mount after all. I just had him change it out. Thanks again for your advice.