QuickA8

Ok to preface. not on the A8

How loud is a bad cat?

This is on an MB E320. I got out of the car today and heard a really bad (loud) metallic noise (sounds like its turning). When I first heard it thought is was the exhaust. Then I am going back and forth between exhaust and Transmission. It almost sounds like its a gear spinning with no oil. Sound coming from the same area as the cats and the trans.

Not noticable till warmed up. Only does it in Park, R, N, D, with brake on. once driving the sound goes away. Shifts smooth, no CEL's, but sound does change with shifts from P>R>N>D.

I know not an audi but this group is so great thought I might catch a break.

Thanks in Advance

DaveInSaltLake

that would indicate the catalyst/ceramic matrix is breaking up.

QuickA8

I couldnt reach my arm up there. I am going to go get some ramps today. I am not at my house and I can only do this on the street. Luckily not a busy one but I almost go run over a couple of times.

I think this thing is lower than the 8. Almost got stuck under there.

Thanks for the reply. I just was wondering how loud a bad cat could be. Sounds pretty loud.

Also really makes the sound when warmed up, and at about 1000 Rpms. So its something that has a resonance.

Thanks again.

A8CT

when mine did the same, it only made the noise when cold and went away as it warmed up

OOOOya

you should hear what sounds like good sized rocks in a coffee can at certain RPM which could change with how hot things are. Drive with the window down along a stretch of road with concrete barrier or even a curb. Those are very effective at bouncing the sound.

If it's something in the transmission, you'd certainly notice bad things with the driveablity.