Is it kind of popping out of joint, then slipping back in?

If so, my jaw's been doing that since I was sixteen, every time I yawn (that gets tiresome!) and so far no one has been able to figure out why, but also no one has ever been particularly alarmed about it. It may just be a new 'thing' to deal with. Still does it, even after cancer treatments. Just started out of the blue when I was a teen. My doc back then showed me how to reset it if it didn't go back by itself (because the first time, it locked into place for a few hours), and that was that.

Not that it's necessarily the same as what your husband is going through, but wanted to share a story to let you know that it might not actually be a scary thing going on ... just an annoying one. Might be a TMJ thing, too, and that, they can help with a little.

I hope you find a good and simple answer!