A team from Cambridge University seems to have the answer why a kettle lets out a whistle as it boils.
Scientists say that as the water in the kettle boils, vortices are created by the swirling of the steam. It all depends upon the speed at which swirls of steam are funneled through the spout as the water reaches boiling point. When the steam jet becomes greater, it gets forced through the small opening and it begins to vibrate and vortices are created.
The science behind the noise the kettle makes when the water boils can offer an explanation to some other disturbing noises like the sound of trapped air in plumbing pipes or damaged car exhausts.
Scientists found that once water begins to boil in the kettle, the whistle behaves like a Helmholtz resonator. They found that above a particular flow speed, small vortices at certain frequencies produce the all too familiar whistle.