Search notes:

Registry: HKEY_CURRENT_USER\Control Panel\Sound

Values

Beep

@reg add "HKEY_CURRENT_USER\Control Panel\Sound" /v Beep /t REG_SZ /d "no"  /f  > nul
Github repository about-Windows-Registry, path: /HKEY_CURRENT_USER/Control Panel/Sound/no-beep.bat

ExtendedSounds

@reg add "HKEY_CURRENT_USER\Control Panel\Sound" /v ExtendedSounds /t REG_SZ /d "no"  /f > nul
Github repository about-Windows-Registry, path: /HKEY_CURRENT_USER/Control Panel/Sound/no-extendedSounds.bat
… however, setting ExtendedSound to no didn't have the epxected result. Actually, I am not even sure what it changed or changes.

Relation to beep service / restarting the computer

The relation (if any) to the beep service is unclear.
Some sources on the Internet suggest to stop or restart the beep service after making a change to this key in order to apply the changes with immediate effect.
However, I found that I could not stop the beep service, the service hangs after stopping it: 
C:\> sc stop beep

SERVICE_NAME: beep
        TYPE               : 1  KERNEL_DRIVER
        STATE              : 3  STOP_PENDING
                                (STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x0
        WAIT_HINT          : 0x0

C:\> sc queryex beep

SERVICE_NAME: beep
        TYPE               : 1  KERNEL_DRIVER
        STATE              : 3  STOP_PENDING
                                (STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x0
        WAIT_HINT          : 0x0
        PID                : 0
        FLAGS              :
Thus, it seems, to me at least, that I have to restart the computer to apply the changes.

TODO

What is the relation to HKEY_CURRENT_USER\AppEvents\Schemes\Apps and mmsys.cpl?

See also

HKEY_CURRENT_USER\Control Panel

Index