I dug a bit deeper and this car has been doing this for about a year and it is intermittent. I have yet to see it happen and the passengers are usually gone by the time I get back down from the mr so I cant ask them what floor they got on. I will check genny voltage my next visit. im thinking it may be rolling when the brake picks to go down. the brake sounds a bit sloppy but ive only had these units under my care for less than a week so it may take some time to get it under control. thanks