radio volume wierd problem

i have a 02 chevy 2500 cargo van v6, while going down the road with the radio on, you cannot hear the radio, but then at a certain place of the footpedal the volume comes on by itself !!! as you keep the gas pedal at this same place it continues to climb the volume until its all the way up ! upon letting off the gas it will shut itself back off until hitting the gas again ! i have looked around the gas pedal and its not in the way of any wiring so i have no ideas, anyone have any? it is a factory amfm radio with NO cassette or cd, HELP!