When the vehicle (2006 Envoy Denali) is running and we are driving with the radio on an intermittent whine comes from the passenger side rear door speaker. The whine is dependent upon engine rpm and rises and falls with rpm. The whine is not constant but seems to depend on whether I have hit a bump or not. Since the whine is not consistent and seems to be triggered both on and off with road irregularities, I believe there is a loose ground somewhere. Anyone have any ideas what could be causing this. I am wondering is the air pump for the rear suspension could be loose but have not checked yet. I have already replaced the speaker in the pass rear door. Thanks for any suggestions.