The intro doesn't loop, and because it has to match the video I'm pretty sure it's just because the entire file was too short. It should be fine to have different lengths for other song files but I haven't tested that yet.
Speaking of testing, I guess I'll post what I currently have.
Only 9 songs replaced so far.
Currently known bug is audio popping in the intro. Trying to figure out the cause. All other replaced songs are untested, and I'm unsure of where you find them in the game (except I know the bicycle music was changed).
If anyone knows where the current files play in game I would love to know.
https://mega.nz/#!ENUQXaYC!4Qtc3K4t8dIk1eny_1llmdSJTEFbKVo6WuNwbuKbKlc
Edit: Just to note I bypassed the looping intro music error by inserting silent audio afterward to exactly match the length of the original file.