Under IPCop (not IPfire !), activating this feature (“Beep when …”) allowed a small melody to be played during the startup, shutdown or restart stages, which was useful for monitoring the status of the firewall.
Under IPFire, this option is inoperative whether or not “Beep when …” is activated.
Note 1: The beep that was added in the last versions of IPfire (connection of the red network) has nothing to do with it.
Note 2: It is possible to find the original function by executing the following commands - thanks to @roberto (but not deactivatable by the subject of this post) :