Nope, you can remove ogg files and/or add your own. A number of people have commented that they don't like Thor -- my initial reaction to parts of it also were not that great, but I actually really like it now. It's one of those ones, for me, where it is so different that it takes a bit of getting used to, but then I really like it after that.
But I realize not everyone will agree, so if you want to remove a track then nothing will be hurt by it.