Using a tone generator on my computer and a pair of headphones, I found that I couldn't easily hear past 15-ish myself, then I started turning up the volume, or playing with turning the volume all the way up, then all the way down. Using that technique, I was able to distinguish noise and high pitches up to 20.2khz or so. So I think from now on, if I hear some whine, I'm going to trust that it's there and not my imagination. Of course, it's also the definition of going deaf, I suppose, that I have to turn up the pitches to such a loud volume to hear them in the first place...