Isn’t this just normal background noise that your brain has learned to filter out automatically from a early age? Otherwise you’d hear your heartbeat continually. My guess is that by focussing momentarily, you’re sort of temporarily disabling the filter and allowing you to hear tiny background noises which could be all sorts of stuff – connective tissue, circulation etc, like a creaking bike.
One explanation of tinnitus is that your neural filter isn’t working right, so you hear a background noise that would normally be filtered out. You focus on the noise, which in turn tells the brain that it’s important, so you listen to it even more keenly and it turns into a feedback loop. Various tinnitus ‘treatments’ are basically about restoring that original ‘filter’ so that you’re no longer aware of the tinnitus ‘sound’ even though it’s still there.
In a totally silent room, apparently, pretty much everyone will be aware of a tinnitus ‘tone’, but in normal life, it’s simply filtered out.
If I flutter my eye-lashes now and focus, I can hear them – in a quiet room – but in the normal way of things, your brain discards the signal as useless information, so you simply don’t register it.
That’s my take anyway. Not a neurologist, audiologist or owt like that though.
