Here’s a cool tip from The Distant Librarian on how to silence the audio feedback you get when using the keyboard to increase or decrease the volume in Mac OS X.

Hold down the shift key while depressing the volume keys will silence the auditory feedback while raising and lowering the volume, but still show the visual cue.

Other cool tricks:

Hold down option while clicking one of the sound keys to access the Sound system preferences.

Get more granular volume control by holding down shift-option while clicking one of the sound keys to increase/decrease volume in 1/4 the normal increments. Normal, the Mac provides 16 volume levels. Holding down shift-option gives you 64 increments.