We had this problem with our X3 as well. After a new starter, alternator and battery it kept doing it. I found it to be a disconnected ground strap underneath the vehicle while changing the oil. I was about to pull my hair out with this but happy to say it's been rectified and zero issues since finding and reconnecting this.
Just a thought.
http://www.bimmerfest.com/forums/sho...4&postcount=10