[tompagenet2]

There will always be people with slightly wider sensory perception than others, but are you honestly saying that you can easily hear sounds "well above" 20kHz? Have you tested this in a double blind test? I know that sounds like a lot of effort, but it would be interesting. You would be somewhat unusual if you could hear, say, 22kHz.

[nullc]

Not somewhat unusual. A one of a kind specimen.

If you test this and hear something, it's almost certainly because the ultrasonic signal is being distorted by your amplifier and speakers and you're hearing distortion products that are ending up at frequencies you can hear.