1997 S90, 130k:

This car has developed a weird vibration/sound. My mechanic says the problem lies within the "rotating mass" somewhere, but so far has not been able to pinpoint it any better than that. The roughness/vibration can be felt while sitting with the car in neutral or park and by revving the engine slightly. Out on the road the vibration shows itself as a rhythmic vibration and rhythmic sound. The sound is hard to describe. It's kind of a rhythmic low humming noise. It comes and goes. Sometimes on the highway we hear it for miles on end. Then it will subside for a while, only to start again later. We can feel the vibration, but it's not super pronounced. I'd say it would be obvious to anyone who is mechanically aware, and even someone who is not would hear and feel it if the problem were pointed out. It's not shaking the car apart or anything like that. The car is just not as smooth and quiet as it should be. My mechanic replaced the motor mounts when he was investigating. This cut down on the vibration/sound but did not eliminate it. I need to track this down and am hoping someone on the board will be able to point me in the right direction.
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Thanks for all the help. DougC ::::: 1981 242, IPD bars and Turbo wheels, M46:::::::B23FT, rebuild has finally started, will go in 242:::::::1997 S90