Sound test:
Immediately after the console's boot up, before the title screen appears, hold Down + Left + A + B + Select. This will add an BGM option to the pause menu, which allows you to select the background music.
Level skip:
Any time during the game, hold Start, then press Select. Release all buttons, unpause the game and just wait for a few seconds to stage being completed. If you do this cheat being in the pause mode, there is no need to unpause then.
