- What makes that hush sound as water heats in my kettle?
When I turn on my water kettle, I hear that familiar "hush" sound as the water heats. What exactly is that? The surface of the water vibrating? Warmer, expanding air leaving the kettle? I know it can't be a function of the water temperature itself because when I turn the kettle off the sound stops a moment later though of course the water temperature doesn't immediately drop back to room temperature. It's also not the kettle alone since it doesn't make the same sound without water in it.