Some of my thoughts:
I've thought about this a lot from time to time, and my thoughts start with the concept that "music" is, at its root, nothing more than organized sounds. That said, the organization that lets us perceive "music" incorporates both biological and cultural elements. The human mind seeks patterns in everything; patterns help us to recognize and classify objects and events, help us predict cause and effect consequences, etc. Our mind will often bend our perception to find patterns that aren't really there.
When I was a hack mercenary bassist, I often viewed music mathematically. After laying off for a few years, I'm approaching it differently the second time around.
Music has rhythmic, structural and tonal patterns, but what we find pleasing in perceiving these patterns is more a function of our cultural upbringing than anything else. Eastern and western music share many rhythmic patterns, but differ in the pleasing intervals between notes that make up an octave. But significantly, all forms of music recognize the octave interval, which may be a biologically fundamental interval.
Stuff we don't like we call "chaotic," and some music is very repetitive. Philip Glass? That speaks for itself. But we also crave novelty and surprise, and enjoy that which balances the two. Even machinery has musical qualities. But what about John Cage? You could still say it's organized, just not note-for-note or with a steady rhythm; it's not really chance (because he sets up the parameters) but not really predictable, either. The most free-form jam operates within certain rules. Maybe Wendy Carlos' "Sonic Seasonings" toes the line between music and chaos -- but I still like to listen to it.
I've read that music hits a spot in the brain that is even more primitive than the speech centers. I saw something in the news a while ago about an archeologist who found the remains of a Neanderthal flute/recorder, reconstructed it and recorded a few pieces. I doubt the songs sounded like Neanderthal music, because who could even imagine the thoughts and experiences that would shape the music of another intelligent species? The best we have now are the songs of whale and birds.
As you might guess, I have a very broad view of what music is.
