I actually don't remember there being any background music besides for some inside the recollection room, the intro, and the dance scene. You can try increasing the volume settings in game, they were originally 60%, 100%, 100%, but I decreased it to 20% while playing because everything was loud, but forgot to change it back before uploading, so it might just be too low.
Edit: I tested out the base Japanese version and it didn't have background music playing either. I think the creator just made it that way.