You're kidding, right? You seriously don't hear anything when you play those .wav files?
Update: Ok. I think those are just bad .wav files. Here's a link to a zip file containing some purer sounds:
http://mdf1.tripod.com/test-tones.zip
When I blast the sound I can barely hear the 18kHz one.
Oh I thought I was way over the hill... the speakers on my computer didn't 'work', but I sampled them thru a pair of studio monitors! (Boorah!!, I can still hear!).. AND yes that would be annoying!