Tips on looping music for games:
An mp3 file cannot be used for smooth loops, as a split second of "data" is always inserted at the start of the track. usually unnoticeable, except for when trying to create a loop. Therefore, you need to use practically any other audio format available. I personally recommend .ogg, though some game engines don't work with it. Converting mp3's to ogg can be done easily online or with conversion software, and should be done before attempting to edit the audio file for looping.