I was playing around with some phone apps that make high frequency sounds. The kinds that only dogs can hear etc. - Don't ask. They were free.
I found I could hear all the tones marked for various age groups (only people under 30 can hear these... only kids under 10... etc.) but one let me crank up the frequency to a point where I really could not hear it anymore. - But it made me feel ill. And now, (from the tones I could hear, I think) I have an annoying "after ringing" in my ears. - And yes the app is OFF! :P
I need some kind of "anti-tone" app now. To get rid of the ringing. Wonder if someone makes that...?
* Searching.... *
Not surprisingly, they charge for those! >:o|