wheel bearing would make a humming noise when you move the steering wheel, especially on an e30.
bent wheel is easy (i've had two), it makes a rythmic thump-thump-thump
unbalenced wheels/tires are easy assuming it's really unbalenced. other than that, maybe something isn't tightened down all the way...
i'll admit it. i didn't tighten down every lug nut after i put my struts on and put it on the ground, i got too excited. a quick tighten and that stopped.