My Son Has A Loud Motor-like Sound In His Head.

My son has a loud motor-like sound in his head. It comes and goes, but he has it much of the time. He can often only get to sleep by driving his car for several hours during the early morning hours, and going to bed at 3:00 or 4:00 am. He can't concentrate during the day because of the noise.

Any ideas for helping him?