What happens when I extinguish a cigarette in a recipient with some water in it ? It goes like pshhh, but what creates the sound wave ? Is it the water evaporating ?
Sound waves can be emitted not only by vibrating bodies, but whenever there are pressure differences as the result of thermodynamical instability. Therefore even putting out the cigarette can produce sound cause of high temperature (and therefore pressure) differences. It's not an event with pronounced frequency characteristics, because the differences aren't in any manner periodic. Therefore is that "pshhh" not "aaaah" (noise not tone).