@jjj:
A couple times, it was if someone was holding down the up or down button and it was just scrolling through the options really fast.
Then the beeping might have been due to overflow of the keyboard input buffer.
I have a system that intermittently seems to go into keyboard "permanent repeat" mode as if a keyboard key was held down. My impression (over 4 or 5 years) is that it happens far less frequently with USB keyboard than PS/2 keyboard, its most likely to happen at startup (though it occasionally happens when the system has been running for an extended period) and it happens more frequently when the system has been powered off for a long period (more than a couple of weeks).