I have tinnitus too. The strange thing about me is that even though I'm profoundly deaf, I have hyperacuity which means I'm extremely sensitive to the sound that I *can* hear. For me, a high-pitched tone is usually enough to trigger painful tinnitus.
So maybe he should take note of not only what he heard BEFORE the tinnitus started, but also what pitch the sound was, and that may help him figure out if this is a trigger.
Other triggers for me are stress, colds, and headaches (which is a vicious cycle.. you get a headache, then ringing which causes my headache to get worse and so on).
-N
