High pitched ringing at night?

Some times late at night (between 12 and 4am) I can hear a High pitch ringing in my ears. It varies from a high pitch ring to a static sound. And when I turn my head in gets louder or dim and sometimes goes away completely, but when I turn my head back I can hear it again. It usually last for about 30 seconds at a time and happens every night (if I'm awake) and multiple times. Please help. Thank you.