As I lay awake last night, for a while there were lots of sounds. If they are not sudden they can help me fall asleep. However if I don't recognize them I try to work out what they are before I get to sleep.
Last night as the air was still I heard trains, plane, cars passing nearby, distant hum of cars and boy racers.
Sometimes I also hear helicopters and a hum of something in the distance.
Sometimes it is wildlife. I have been pleased recently to hear an owl a couple of times.