Thanks for posting. Googling elsewhere it seems only about 5% of tinnitus is objective as in being audible in a stethoscope or similar. Though it's remarkable how sensitive the ear is. Apparently at the threshold of human hearing the vibrations at the basilar membrane are of the order of 1/1000 of the width of an atom so I guess there could be stuff going on that you can't pick up with a microphone/stethoscope, perhaps.

http://www.nobelprize.org/nobel_prizes/medicine/laureates/19...

Yes, it is indeed very rare and exceptional.

I did some more reading on how the ear works and I think my comment on there being positive feedback is wrong. Looking at how the bits are laid out and wired up it looks more like it uses amplified negative feedback in the manner of an op amp. The diagram I looked at is in Purves et al, Neuroscience 5th edition. I'm now thinking the tinnitus may be from the input maxing out when the negative feedback breaks. From a practical point I've found carrying wax earplugs helps my ears recover.