The only thing I can think of is that it might be too long. (Perhaps more than 10 minutes. Though, I’m not sure if there is a limit on how long can the music be or not, but it may factor?) Or something happened when you installed the mp3 tracks; turning it silent, so you might want to re-install the tracks, or the files are incorrectly named. Other than that, I’m out of ideas, sorry. :(