My 2 cents (and probaly not worth every penny): When I read just the first two sentences I am reminded of a couple of problems I have had that gave me the same vibration results (not on an X5 though) ... lost wheel weights, and a badly mounted wheel on the hub. Perhaps start with those ... simple and cheap. Also, again not the X5, I have had axle grease splattered everywhere from an overfill (including the ABS sensor FWIW).

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2003 X5 3.0 - Original Owner