The loud noise I sometimes have heard upon waking up with a start was unrelated to that experience. It is also a rare experience but it has happened more than once, perhaps no more than 10 times in my life. It wasn't a bang; it was as I described, an echoing door slam, like the sort of noise you'd get from hard slamming a 10 foot high heavy solid oak door shut in a large stone room, where the sound is heard reverberating for around 10 seconds into wakefulness. That isn't something bio-mechanical.