A voicemail or message left on an answering machine that is nothing but a few seconds of dead air.
Left by people who cannot, for some inexplicable reason, hang up the phone BEFORE the end of the outgoing message, but instead wait until the recording begins.
Lisa calls her friend Eric, and reaches his voicemail. Lisa has no intention of leaving a voicemail, but listens to the entirety of Eric's outgoing message (including the beep) before hanging up.
Eric's voice: Hey there, I'm not around right now. There's going to be a beep in a few seconds; you know what to do.
Lisa: .... *hangs up telephone*