Sun Microsystems hardware would halt processing to beep the console speaker for half a second; I worked on a military communications system whose throughout would throttle to nothing whenever a long series of beeps occurred. Wiggling the mouse was enough to flush the alerts:

    "BEEEEEP...BEEEEEP...BEEEEEEP...beebeebeebeebeebeebeebeebeebeebeebeep"

and message processing throughput would return to normal. Operators in the field were trained to use the mouse for this purpose.

Edited to add: the programmers were aware of the problem, but there was a system level requirement that alerts must be audible and that's how Trusted Solaris worked until well into version 8.