Not sure from your description, but I randomly heard a series of static-y beeps from my turned off radio while taking a trip with my wife. Based on feedback from this forum, we confirmed that it was due to my wife having a Sprint cell phone sitting in the open ashtray while we drove. (I do not hear any noise with my Alltel phone). It appears that Sprint and maybe some other cell providers broadcast a frequency/signal that interacts with the electronics in the radio.

Guy