This is a form of tinnitus

Yeah! I have had this as far back as I can remember, and recently found out that (I think) it's tinnitus.

Interestingly enough, it doesn't really bother me unless I'm seeking it out, so I wonder if my young brain just adapted to it.

Another weird fact about me is that I can hear things (I'm 35) that lots of people can't. I can definitely hear switching power supplies in everything (well, almost everything - really high quality electronics mostly seem to be exempt). I also know when bats are around, because I can hear a "clicking" noise from whatever their echolocation-producing organ is. I don't think I can hear the echolocation itself, but there is a very distinctive clicking that they make in the process.

I’m the same age, and also seem to have heightened hearing at this range. I went to an audiologist for a tinnitus flare up, and did an ultra high frequency hearing test, which confirmed I had abnormally good hearing at 8-16k.

He told me that many audiologists in this specialty believe there is a class of people with sensitive hearing, who are more perceptive to threshold changes in hearing (hence tinnitus). But there’s been no real research on it.

I’m not sure to what extent I believe it (given audiology is somewhere close to physiotherapy in terms of rigour)

For what is worth, my situation is exactly the same. Although I never noticed if I can hear bats

Cool. Maybe resonance with their echolocation waves.