Try trashing the com.apple.universalaccess.plist and com.apple.VoiceOver.pronunciations.plist files in your [username]/Library/Preferences folder. And then restart your computer.
Anyway you could record and then upload the sound? It could be a third-party program that's doing it, but without hearing it, it's hard to tell.
ndo you have any odd programs installed? install anything recently?
I'm also having this issue, it is very annoying. I can only hear it when I try to write/click where I'm not supposed to...is this a feature? can it be turned off?
Tried the Universal Access options but still get the beep...
Had the same problem and found that text to speech had assigned the key I was having problem with to "speak selected text when the key is pressed".
Thanks for the hint.
Also for other users, check if the same issue replicates within different profile.