[Pdwight]

First let me say I am by no means an expert on this, just offering some suggestions. First try one light assembly out so you can try each side independently of each other, narrow it down to one side if possible. Second treat it like alternator whine in a stereo...it is after probably spurious AC being generated and getting back into the cars system....try attaching a .01 , .05 , .10 , .50 capacitor from +12V to ground and see if that might trap it and bleed it to ground before it gets back into the car. Next step would be to try making a LC circuit out of a inductor and a capacitor to also act as a choke. I Will try and do some research for better values. We have enough talent on this board we should be able to kill this problem