Rumbling noise from car while driving...
 

While I'm driving around town in my 960, I hear a rumbling noise. Kind of sounds like a baseball in a metal bucket. As soon as I come to a stop, the noise stops. If i'm on a very smooth street I can not hear it. I also can not hear it on the highway because of the wind noise. But around town it just sounds lile something is jiggling around. I think it's coming from the front but not 100% sure. Any ideas?