I guess music, like beauty, is in the eye (or should that be the ear?) of the beholder (belistener?). There are those who maintain that the sound of a well-tuned car engine is music to the ears. I've never thought of it that way, but then I've never been mechanically inclined. De gustibus non est disputandum...
Be that as it may, here are a few musical "instruments" that challenge one's definition of that term. I find the first three interesting and enjoyable in their own way; the last one is more of a stretch, but I think it's still creative. Musicians may disagree.
How's that for stretching musical horizons?