The most different noise I've heard (usually at seminars, sometimes from a visitor) is a kind of yipping and/or yapping sound: "y-i-i-i-i-p-p...." and "y-a-a-a-a-a-p-p..."
Sprinkle a couple of those into a usually quiet dojo, toss in a few Kiai's, and pretty soon there'd be a supressed giggle or two.
Of course, there are also the senior students who manage to make an encouraging "yes, that's it, yes" comment on technique sound like the sound track from an adult movie
