I'm *fairly* sure there's no music. The weird thing is, I remember some music playing, but I could never emulate it (possibly, could just be a confused memory).
I'm guessing, if there IS some short theme, it doesn't always play.
EDIT: I just tried stopping somewhere and sleeping, and also making camp and sleeping. Unless you run into the 'earth pig', Arne, there's no music. Just birds as well as the 'wind seashore'. Of course, there could be a specific that causes it, like I said