Seen recently when on a morning walk near to home; wood ducks as they're commonly referred. They'll often fly up into the gum trees; quite high. My Readers Digest Birds of Australia book tells me their voice is: nasal 'mnow'. Guess you'd have to be an ornithologist to have got that one together. I can piece it together to the sound of the duck, but I'd never have thought to describe it that way.