My guess is that it's grounded near your antenna. When I installed my fog lights I grounded them to a bolt on the frame in the engine bay located close to the antenna and I got some static when they were turned on with a few FM stations that had a weak signal. I just noticed this a few days ago so I haven't relocated that wire to see if that's exactly the problem or not, it's just a theory though. I also have a bullet antenna, not sure if that makes a difference.