Comment 52 for bug 290204

This too is a fix (used on Jaunty):

In the terminal, perform the following:

      gksudo gedit /etc/modprobe.d/blacklist.conf

Then add the following at the bottom of the file:

      blacklist pcspkr

Now restart your machine. Note that the beep will still sound when shutting down. However, once restarted, try shutdown again. The beep(ing) should now not occur.