What Causes Grinding And Cracking Sound In Ear?

Recently, for about the past 2-3 weeks, I've been hearing this grinding/cracking/gravelly sound in my left ear; this only happens, however, when I turn my head from side to side, when I crook my head sideways both left and right, or when I make abrupt head movements. I am young and lead a healthy lifestyle, and there's no pain or discomfort in my back or neck, so I don't think it could be attributed to spine problems... I also don't think it's fluid inside my head because I have no sinus or ear pressure/pain problems, it's just that the noise is very annoying and I can't hear people talking to me in my left ear when it is occuring. Do you know what might be the problem? Thanks.