It depends on your age and, to some extent, your ethnicity. As we get older, we lose our ability to hear high pitched sounds. Aboriginal Australian's ears have a wider frequency response than Caucasians. I don't know how it works for other races.
What would be interesting is if everyone listed their age and background.
Interesting NYT article here.
It outlines one of the most famous use of this frequency-response disparity. A few years back, a Welsh security company used high-pitched sounds, inaudible to adults, to keep kids from congregating outside shopping centres. It would affect the kids, but not the older people.
Kids used that tone, instead, as a ringtone for use in situations where you wouldn't want adults knowing you had just got a text message (in class, for example.)
The street finds its own uses...