The sound is back so I did the experiment now, updates are there.
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.
As someone with some tinnitus myself I've been tempted to try that. The usual explanation you see of tinnitus is that the sound sensors break and then the nervous system makes up sounds to compensate but that's never really made sense to me. Usually if you don't get input to the nervous system because say a limb goes numb or you lose sight you don't get that kind of effect.
The ear seems to have a built in amplifier using positive feedback - the "cochlear amplifier is the outer hair cell which increases the amplitude and frequency selectivity of sound vibrations using electromechanical feedback."(Wikipedia). I wouldn't be surprised if that mechanism goes out of wack and makes a noise in the way that you can get a squealing feedback from a public address system when the gain is set too high. I'm not sure that's been experimentally tested in a way that makes if clear if that's a thing or not.