It is the ride height sensor: I suspect you have Xenon lights installed. Xenon projectors self adjust so if you go over bumps/imprefection they compensate for the change and avoid (to a certain degree) flashing other cars. That's why they cycle up and down when the car starts.

Good to know that's what causes the turn signal light to come on, in case it happens to me: I would have probably gone insane trying to figure this one out

Pretty stupid they unplugged it instead of replacing it...