[gentoo-user] [OT] High-pitched sound from inside the PC when opening menus

[Nikos Chantziaras]

This is a question that is off topic of course, but I'm not sure *where* 
it would be on-topic.  Considering that Gentoo users are also often 
so-called "enthusiasts", I'll drop the question here ;)

In KDE (3), when enabling the "fade" effect for menus, clicking on a 
menu results in a faint, high-pitched tone coming from somewhere inside 
the PC case.  The tone lasts for the duration of the fade effect (should 
about 0.2 seconds).  This is happening on more than one machines.  You 
have to listen carefully to make out the sound, but it's there.

So the question is simple: where does the sound come from and why?