Sometimes when Iim involved in a presentation, I need to change the volume on my PowerBook. I like having the "bloop, bloop, bloop" of the volume feedback active so I have some idea of how loud my speakers are, but that sound can be distracting when you or someone else is trying to teach. I avoid the problem by holding down the Shift key while I use the F4 and F5 keys to lower or raise my Macis volume. This trick temporarily mutes the volume feedback without disabling it in the Sound Preference Pane, and avoids the alert sound beep you get from the Volume menubar slider.