:) you can always check with going deaf, I have my doubts its that though
http://www.freemosquitoringtones.org/hearing_test/
Anyone who wishes can also use it to compare the sounds they hear to the sounds available there, its a hearing testing with the different higher vibrations we can hear.
Personally I can hear all of them, although the last took me twice to hear. My mother cannot hear past the fourth, however
I can often hear the vibrations of the things around me if I listen for them, sometimes the inner current does come out and I hear it loud and clear :)
A few of my friends have some things where they can hear their ear hairs dying, also high pitched.
Go with what rings with your gut,
as each time you hear the sound, it may vary, it may be different, thus it may have different sources.
My kindle, which I keep with me a lot, produces around 20 thousand Hz, very occationally I'll tune into it and be able to hear it, othertimes it may just be my ears reacting to it.