I was with you until: "[...] but it can also be heard by the examiner (eg, by placing a stethoscope over the patient's external auditory canal)." and now I'm even more confused

Poorly shielded electronic devices go BRRRRRRRRRRRRRRRRRRRRRRRRRRT EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE!

About 2/3 of my family (including me) have the same thing, some kind of hereditary issue with the nerve that runs from the jaw up behind the ear. Accompanied by most of us also having jaws that don't quite fit in their sockets properly and tend to pop and crunch from time to time.

If you close your eyes tightly you can induce the perception of color. If you stand in a doorway and lift your arms to the side so that the backs of your hands are pressing against the inside of the door frame, keep pressing for 60 seconds, then step out of the doorway and relax your arms: it'll feel like your arms are floating.

The body's systems are complex and part of reliably filtering signal from noise in such systems is establishing a baseline while in a steady state. Our brains are pretty good at filtering out noise but the pressures or degradations which lead to tinnitus seem to trick the brain into accepting some noise as signal.

If you're looking for a deep dive then the following paper does an excellent job of outling what we know and what our best guesses are so far: https://www.sciencedirect.com/science/article/abs/pii/S0306987724002718

It's jargon-laden but nothing someone armed with a dictionary can't handle. 🙂

Maybe it's like the way microphones and speakers are basically the same hardware, with the cells surrounding the hair in your ear canal vibrating those hairs "out" at high frequency for some reason.

Somebody much smarter than me will be able provide answers!

The hair cell's whole job is to send neuronal signal when there's vibration at its specific frequency. It's entirely conceivable that a cell would get stuck in the ‘send signal’ mode when damaged, just as it can go the other way and send no signal ever anymore.