When i open my mouth about half way and chew in the air, my left inner ear makes a sound like there's sand grinding in my ear/jaw. any ideas?

TMJ: It sounds like your tmj. It. Could mean that the joint has a dislocated disk, a rough fossa, or the joint could be arthritic (very unlikely). Anyway i would tell you that if it bothers you enough go see your dentist or an oral surgeon.

Crepitus: The noise you are hearing is termed crepitus, and it may be a sign that your jaw joint is undergoing some degenerative process. See a doctor who is comfortable and knowledgeable about treatment of TMJ disorders.