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I've never heard anything like that before. It's hard to even guess without putting an ear under there and following the sound. I would be just grabbing at straws but it could be a chattering relay but I wouldn't know where to start without some schematics and following the sound.
I don't know what the wires are for but if it were me I would disconnect/remove any aftermarket wiring in that area or associated with the lights and see if that does anything.