You can test your hearing with the tone generators in Winamp or Foobar.

Flac stuff is here.

Below is a 17,500Hz pure tone.

When I use foobar's tone generator, I get some sort of weird noises once I hit about 18,500hz. Is there a flaw in the tone generator or is it likely an issue with my setup?

I can hear everything up to 18,500 so I'd like to be able to test a little further than that to see what happens... of course in order to hear 18,000+ I need to jack the volume all the way up to max on my sound card.

Probably the soundcard is the guilty. Try 48Khz sampling rate, changing windows' audio settings (something like "sampling rate conversion quality" - don't know the exact name in english windows version) or lowering volume in mixer (Wave / Volume Controll).

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Edit:
Pseudoacoustic,
according to CoolEdit's spectral view and frequency analysis your sample contains more than only 17500Hz (-5.11 dB):
1898 Hz: -77.41dB
6 lower peaks in 3000-10000 Hz range
10990 Hz: -73.5dB
14900 Hz: -73.05dB
3 peaks > 17500 Hz, among them
21390 Hz: -16.39dB

The lower frequency content is clearly audible so better use the sample I've uploaded.

2 More "How high can you hear" threads:

How high can you hear?

How high can you hear (with music & lowpass), ABX required (with real music samples)

Beware of your tweeters! With continuous, loud, high frequency tones, it's very easy to fry your speaker tweeters, has happened to some people here. Better use short, faded-in and out, test tones.

Maybe like this (-> sample):

That one would be good, good editing. However, I would try to space a little bit more the tone bursts, just to be safer about not frying the tweeters.