Cycle to the number of the music you want and press A + B simultaneously. This is very difficult to do. If all you hear is a long hum, that's not it -- try again.

Once you've accomplished this trick, the music will correct itself. If the music changes significantly, you press A or B while SOUND or VOICE is highlighted, or sometimes when the music cycle starts over. The music will still be the same tune, but the sounds are altered.