I’m not sure when it started but I recently noticed that my screen was flashing all of the time when I was using the terminal instead of sounding a tone like it should. I dug around in Terminal’s preferences and in Universal Access but everything seemed to be in order.
A couple of Google searches later and I came across a post from Erik Phansen that solved my problem. It boils down to running one command in the terminal:
sudo killall coreaudiod
Note that I had some strange feedback echoes after killing coreaudiod that I fixed by alternating between starting iTunes and playing some music and killing coreaudiod. Unfortunately I can’t say what combination stopped the echoes.