Ubuntu: Disable System Beep

To disable system beep in Ubuntu permanently:
1. System -> Preferences -> Sound
2. Under the System Beep tab, uncheck Enable system beep


To disable system beep in Ubuntu temporary:
1. Open terminal (press Alt + F2, and type in gnome-terminal)
2. Type in the following command:

xset -b

3. Now the system beep is disabled until the next reboot

Ref:
Turn off (mute) system beep - Ubuntu Forums
VMware Communities How can I quiet down the guest system ...