Research indicates that (some) orangutans make wind 'instruments' out of folded vegetation, blowing through it to modulate the sound of their alarm calls (reports here and here). This makes them the only animal apart from humans known to use tools to manipulate sound.
I happen to be researching (and attempting to write about) the origins and significance of human music at the moment, so especially enjoyed this. As Robert Shumaker of the Great Ape Trust says, "It's really, really nice to see an example [of tool use] that has absolutely nothing to do with food."
(see also the funky gibbon)