This is probably Tinnitus. If it comes and goes, it is most likely Pulsatile Tinnitus (like mine was, to the sound of my heartbeat). Tinnitus could be caused by one of many things, so it's best to go to your doctor or an ENT and get checked out first to rule out anything serious. I got CT scans, MRIs and hearing tests and after 2 years finally figured out that it was my neck muscle (SCM) that was the problem. As soon as the tension "released" (in my case, the muscle essentially snapped, ouch) the Tinnitus was gone. Check out TMJ and Tinnitus, you could try to go see a dentist that specializes in TMJ or even a chiropractor.