So, i've been testing this quite a lot, and also, comparing it with other working / functional music mods that dont have this issue of crashing or music freaking out. It seems like, you gotta convert the mp3 files to ogg (i dont know about any other format, i just tested on this one), and it solves the problem basically, or at least it did for me.
I dont know if its a problem with mp3 format, but there you go, hope it helps