Are you still young or do you have old man/old woman ears? Click on the link at the right side of the wikipedia page to hear it...or not
http://en.wikipedia.org/wiki/Mosquito_Ringtone
So a little experiment.
I hear it fine.
I brought my wife in and started the sound loop. She never flinched. I told her about it and then started it. She can't hear it. Even stood right by the speaker but nada. (I told her she has old lady ears.)
Then I bring my 6 year old son in and start it. I never told him about it, he immediately grimaced and put his hands over his ears. I asked if it hurt and he said not really a hurt but more like fingernails on a chalk board.
Pretty wild. Especially since I can hear it with my gun shot/loud music listening to damaged hearing.
My dad looks at me like I'm nuts when I play it for him, he says I'm messing with him.
One of my teenage patients grimaced when she heard it a few minutes ago.
Weird.