Disable the annoying PC speaker in Ubuntu

Temporarily (doesn't require a restart):

sudo modprobe -r pcspkr

Permanent (requires restart):

sudo your_favorite_text_editor /etc/modprobe.d/blacklist.conf   #text editor can be anything from "vi" to "gedit", whatever you want!

Add this line to the end of the file: "blacklist pcspkr"
Reboot!