Turn off the system beep in the terminal without X11 use:
kbdcontrol -b off
Turn beep on outside X11:
kbdcontrol -b 100.100
Turn beep off in X11:
xset b 0
View the bell settings with sysctl before turning off system beeps globally:
sysctl hw | grep bell
hw.syscons.bell: 1
Turn off bell until reboot
sysctl hw.syscons.bell=0
hw.syscons.bell: 0
To change the bell to 0 and keep the setting through a restart, add this line to /etc/sysctl.conf
hw.syscons.bell=0