Open the machine door.
Log in with the admin password (default: 888888).
In the main menu, select System Settings.
Then go to Android Settings Menu.
Scroll down to the Sound or Media section (depending on software version).
Turn off the background music by setting the volume setting to 0 or by disabling the Music Player.
Click on Confirm / Save to save the setting.
Restart the machine once.
After the restart, there shouldn't be any more music playing.
Note:
If you want to turn the music back on later, you can go the same way and turn the volume up again.