mediasteam

I have been experiencing my car vibrating as soon as I change the gear on Drive and humming noise coming from underneath the car. I know it is not the wheel balancing or tire rotation problem b/c I have done that all and they should only occur in motion.

My car is 2001 E320 Sports with 45,400 k miles.

Anyway, I took it to a mechanic who does my oil change and asked him to take a look at it. He told me my motor mount looks new so that must not the problem, then he said transmission mount needs to be changed (for aound $150 parts and labor) He maybe right b/c my car jumps a little when i change gear from parking and in rough road gear box shakes.

He also told me that catalic converter is no good which needs to be changed and suggested that I make an appointment with Mercedes to have it changed b/c they should do it for free within first 8 years or 80k miles. Does anyone have any similar experience? What is a catalic converter? and from the problems i'm experincing does it sound like it might be Catalic converter problem? Any suggestion would be appreciated. Thank you!