Under body rattle/pinging when car is in drive.

Thank you for taking the time to share your advice Mercedes Connexion from Cupertino, CA.

That's very good advice, Steevie. Thank you. There's no dummy light lit on my dash.

I hope its a heat shield but I've never seen one loose on a 300 yet. The catalytic converters break inside their housing on a regular basis (the honeycomb seperates from the outer casing, hence the rattle). Usually the left side for some reason. I've had cars come in with broken cats and they usually don't set the check engine light as the honeycomb is still doing its job-just noisily. I've even had them fail emission testing because they are inefficient and still no light. Let us know what you find, I'm curious.

Hello Mercedes Connexion: Thanks for your follow-up re: the light on the dash. I need to get the car on a lift and do as you suggested in your first reply. That will help resolve the issue. I'll definitely let you know how it all sorts out. Much appreciated...

I'm sorry then it's like the jeeps that do that , Yes , I know , ok ..