Brian - after reading your post I have to say that I'm experiencing almost identical problems with my C280. Although they are different cars, your symptoms are virtually the same as mine. My C class is currently at the dealership being diagnosed. So far no luck, everything checks out... although they admit the vibration is there. Look up my post C280 Going off a cliff....

I'll be watching your progress!

Mark E.
Ft. Lauderdale

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Mark E.
Miami, FL
2 X 1997 C280