Why does my jaw feel hollow lately?

Recently I’ve noticed that occasionally my jaw, teeth, and skull have a strange resonance. When I click my teeth, they make a weird hollow sound. Same thing happens when I tap any other bone in my head. This is a fairly recent phenomenon, and isn’t constant…usually occuring for a couple of days every couple of weeks. I’m not the only person that notices it, my GF can hear the difference as well, soI dont think it’s just a matter of how sound is traveling to my own ears…unless she’s only thinking she’s hearing it, which is entirely possible.

On an unrelated note (I hope) - my girlfriend seems to think my teeth have become more crooked (shifting a bit to the left). I noticed this myself before she ever said anything.

Are these two things possibly related?

Has anyone else encounted this “hollow” jaw situation? Should I be worried?

How old are you?