The Sound of Silence
You do realize, don't you, that if you are in an office full of computers that chime in unison for e-mail, that you could probably stealthily mute all of them in one way or another, and nobody would know how to restore the sound!
This also explains the habit of leaving the phone on the desk when attending meetings: the average drone has no idea how to mute the phone for a meeting, so leaves it behind instead.