Brand new Windows 7 box loaded with the usual dev tools -- VS2008, Firefox, Chatzilla, Thunderbird, emacs, Pidgin, Putty, iTunes, SharpReader.

Every couple of minutes, I get an audio notification consisting of three rising
notes, maybe a middle-C-G-F on a piano (I don't have a piano handy, and don't have
time to use GarageBand to try to figure it out).

Nothing in the notification bar is flashing when this happens.

The sound isn't in any of the Windows Sound control panel applets. And it's not
in C:\Windows\Media, so it's most likely coming from a non-Microsoft app.

Any chance it's Pidgin when the status one of my contact's changes (which happens plenty frequently)? Oh, look at this --- Tools/Mute Sounds. Let's try that and see what happens...

Is this familiar to anyone?