What evidence is there that we hear Ultra Sonic audio?

[boromir]

I had my ultra subs on while sleeping, and my son came barging through my door and went straight to turn it off my player because it was too loud and annoying for his sensitive ears.
Young people can hear it easy.
I have heard stories that after banning cell phones in class, kids started using ultra high freq. ring tones because so other kids could hear them, but teach couldn't-amazing.
I wish my ears were that good!