What makes you think a bulb should be moving left/right etc? Are you getting confused with cornering headlights that self-adjust when turned on as opposed to Xenons which are a type of bulb?
Unless they're cornering lights, there's no reason for headlights to move side to side,
mine dont stop moving.. you can hear em adjusting all the time! getting on my nerves now! where on the rear beam is this sensor?