Why am I getting radio signal interference when my car is running?

your noise suppressor went bad. they go in the power line to the radio. rhe sounds you are getting are from the alternator charging. also the internal noise supressor could have gone bad in the alternator. this is not un common and an easy fix. radio shack etc carries the suppressors and they work well. also there is a ground fault suppressor that made a world of dirrence in a car stereo i once put in. had no sound distortion at all after installing.