"whirring" sound coming from speaker

[wideawake]

Hi all,
I heard a "whirring" noise in one of my speakers in the back left passenger door. The whirring noise gets louder consistent with the amount of pressure put on the accelerator. I removed the door panel and disconnected the speaker. However, the whirring sound is now coming out of a different speaker on the opposite door! The whirring sound only occurs when the radio is on. A bump in the road may cuase the whirring to either stop or start. This sounds like an electrical problem to me; however, I have no clue where to begin to rememdy this problem. Can anyone assist me with suggestions? Thanks in advance!
Jeff

 

[Moose]

Check your negative battery ground, and other ground straps you can find. I want to say there's one near the alternator that can cause the tachometer-based whine....