Oh, it's Canadian cloud penetration detector. It's fitted to Q400 too but I'll be damned if I know what is whistling when you get her inside a cloud. I'd guess it's those long wipers' arms.
The ice detector uses a change in frequency on the tip of the probe to detect ice so is suppose that is also what is happening to the whole airframe?
Not quite... the ice detector vibrates and as it gets iced, it gets heavier and vibrates slower - that's change in frequency that triggers icing alert, it has nothing to do with acoustics.