That repeated "song" that's played upon starting up the game... is there a way to change it? I searched through the Data>Sounds but it wasn't there. Is it possible to change that in-game sound?

Can no one answer this for me? There must be a music file somewhere!

It's in the custom tori folder

You need to purchase a "music" item from the torishop, from there you can change which song comes on and upload you're own music to toribash.

For an alternative solution you can go into options and turn the music volume to 0.