I used to fall asleep to whatever ambience I could find that wasn't 10 hours long (seriously, I'm not gonna sleep for 10 hours the whole time and I don't want it frightening me when I wake up) but nowadays I'll just sleep in silence.
Ambience usually just comes from whatever game I'm playing, and it's really nice to have. Either it's really pleasant, or very spooky, depending on the game, and I enjoy that a lot. Adds to the experience a lot.