One cause of tinnitus is a blood vein/artery, I can’t remember which, that runs too close to the surface near the eardrum. It can be fixed with surgery, but is very expensive and dangerous to boot.........
I'm unusually vascular (I'd make a good lab dummy). The noise does seem to pulse with heart beats and that would explain the sound variances when I move my jaw. Also, I probably have circulatory issues and any blockages can certainly create friction or a ventura effect (like the increased noise from a dirty air filter).