what is this loud sound underneath the rear of my car when I drive ? on 1993 BMW 325i

the faster I drive the louder it gets

by in Dallas, TX on April 14, 2013
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1 answer
ANSWER by , April 15, 2013
Bad tire wear (cupping on inside tread?). Rub your hand over the tread in the direction of rotation and see if it has high/low spots.