What do you call the round plastic whistles that go "weeeeeeeeeeee" when you blow, instead of the usual whistling noise. Sounds like a noise you'd hear at the circus.
I think that you're all wrong. I remember a Christmas cracker toy which was a conventional tubular whistle but had a turbine inside. When you blew it produced a whistle but the turbine gave it an increasing volume and vibratto. How's that?