I have a similar issue (I'm not sure if I grind or just clench my teeth), which leaves me with tension headaches and a constantly popping jaw. Unfortunately, I tend to also clench my jaw when awake and I have to consciously remind myself to relax. I have even started a weird habit of keeping my tongue or cheeks in between my teeth so I know when I starting to clench.
I am new to paleo/primal and have been easing into it. I have cut out sugars and most processed foods. I just finished a 30-day wheat-free challenge and, to see if I noticed any affects, allowed myself to have a few meals with wheat in them.
Two days after my first meal that reintroduced wheat, I woke up with a sharp pain in my jaw and it was so sore I didn't want to open my mouth. It was that morning that I realized I hadn't had much jaw pain and the frequency of headaches had tapered off during my wheat-free challenge.
While I know stress and other variables can play a role, I am cutting out wheat again because I feel that wheat intake negatively affects this issue. Life without jaw pain and with fewer headaches? Sign me up!