Yes could be TMJ (forgot the name before).
You say you have no pain, but have you pressed with your fingers really hard around the outside of your ear on the jaw near the hinge and down. Also above the ear on the side of the head?
Evidently there are many muscles that can contract and stay contracted unless you manipulate them.
Have you visited a physio that also specialises in TMJ? If they do acupuncture (mine did) they will stick needles into the contracted muscles which makes them release. Good fun, but works over a few visits.
Also did you try a course of Celebrex (my specialist recommended this in case the joint has inflammation.) If you have arthritis in other joints you could well have it in your jaw hinge joint too.
I told a friend who got ear trouble and specialist couldn't find anything to press around his ear jaw hinge, he said it didn't hurt, I said press real hard, he said it hurt because he was pressing hard. So told him to press the other side as hard and it didn't hurt. There you go. 🙂