Cacophonous.I think maybe the first man-made music would have been crude to our ears, no? I don't mean to sound elitist, but think about it: music is a different experience for different cultures. As a culture, Westerners/Northerners think oriental and middle eastern music sounds strange because the musical tradition has a different evolutionary path. Yet, to those cultures, these sounds are familiar, comforting and beautiful. I think that might be a somewhat valid perspective in reference to your though/question. Whatever the first man-made music sounded like, in order to be an appreciative audience, we would have to listen from the viewpoint of the creator's current knowledge, biases and experiences.