strange noise from under car
 

At first I thought it was the brake dust shield rubbing so I took all 4 wheels off and tested. Not it. While I had the car up on stands I released the brake, cranked the engine and put it in drive and still got nothing. Put everything back together and cranked engine and I could hear it again, but while carr was on the ground and in P. The sound is sort of a rubbing noise. It isn't continuous though. It doesn't sound like hard metal either, it sounds like a thin heat shield type metal....or something hollow. I'm wondering if its the exhaust. I know its not the wheels rubbing since I can hear it when the car is in P and I tap the gas a little. Any thoughts?

I had that problem on mine. I replaced the exhaust system and it went away.

what was causing it?

found out what the problem was......something in the catalytic converter is loose. I will take it to my muffler guy tomorrow to have him look at it.

Rattle in the cat? Probably media failure. Usually caused by bad MAF and/or O2 sensors both of which cause rich fuel mixture and overheating of the cats.

I have not gotten any codes from my CEL. Wouldn't I get error codes if the O2 was bad? Or the MAF?

Could be the heat shield is just loose and needs to be welded. Happened to my old 1993 300E (3.2) "E320".

OBD codes probably. CEL maybe not. If you have a scanner, check for stored codes. Then erase them and see what comes back after a few drive cycles. If you don't have a scanner, consider getting one since they are fairly inexpensive and easy to use.