First, get a music file that you would like to hear in the game and change it into a .mp3 file. Either cut or copy it. Find the "main" folder in the game directory. Enter the "sound" folder, then enter the "amb_stereo" folder. Paste your sound file in that folder. Find the sound file for the level that you want to change. Then, switch the names of the two sound files. You will now hear your favorite songs during the game, but other players will not be able to hear it.