To enable or disable bell use MIB hw.syscons.bell on FreeBSD operating systems. To set MIB on FreeBSD use the sysctl comamnd line utility, which retrieves kernel state and allows processes with appropriate privilege to set kernel state.
Disable bell with systctl command
Type the following command to disable for current session:
# sysctl hw.syscons.bell=0
Make sure settings remains same after you reboot the laptop, enter:
# echo "hw.syscons.bell=0" >> /etc/sysctl.conf