undercarriage rattling- cat. converter? 97 e420
 

My dad has a 97 e420 which has an obnoxious rattle coming from under the car, about half way back. He says it has something to do with the catalytic converter, and it is a big, expensive job to fix. It only makes the noise when the car is in gear, not when it is in park. Anyone else experienced this type of problem? Something doesn't seem right to me, but I can't really go under there to check it out because it would seem as if I was second guessing him. Thoughts?

Sounds like possibly a heatshield.
You'll just have to look under the car when your dad is sleeping.
Put a sleeping pill in his drink, if you have to. :D

I had a similar rattling in my car, and it was the heat shield.

Only took a few bucks to have it welded back in place.

Get some steel wire, baling wire, and wrap it around the shield. That worked on a Ford Explorer I once had.

On a Mercedes ? Shame on you.
:D