[s4iscool]

computer? I get it even when the volume is muted, and something like MSN messenger wants to tell me its no longer available after putting the PB to sleep. I hear it other times as well, but its really annoying, especially when the volume is muted, and you still hear it.

[himself]

go to your System Preferences and click the Sound pref pane. In the Sound Effects tab, adjust the Alert Volume to something more to your taste.

Also, is your audio output through you computer, or do you have it playing through an external source? If it is the latter, that would explain why the sound is audible even when it is muted, but you shoudn't hear anything otherwise.