I’ve always learned it comes from damaged hair cells inside the ear, how could it be anything but physical? Very surprised it can be picked up with a microphone in an anechoic chamber though
Why would a damaged hair cell make noise?
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.