Well there's mouth music, lilting, scat singing. They've all got sounds which are sung, and you could write down as if they were words, but they aren't words.
And then you can have words spoken rather than sung, but with a musical accompaniment. Talking Blues for example. I think we'd probably tend to refer to these as songs.
And I'd call humming the human equivalent of the kind of siongs birds and howler monkeys make. Probably predates spoken language. In fact I tend to think that our ancestors probably sang words before they got round to speaking them.
An interesting topic, CarolC. I'm starting to look out for your name in threads. Welcome to the Muidcat, if noone has said so up till now. They probably have.