Why does it appear on tv screens as a mix of grey, black and white, and what creates the “shhhhhh” noise? Seems to me if there is no signal coming to the television, there should be just a blank screen, no?
There is a signal coming to the TV. It just happens to be rather random in nature. I am not sure where the bulk of it comes from but some of the static is caused by the reception of cosmic background radiation that was created during the Big Bang.
http://longplastichallway.blogspot.com/2005/08/tv-legitimate-religious-experience.html
The “shhh” noise is the audio equivalent of the random visual static. White noise has an equal energy distribution across the audio spectrum, while the slightly cosier pink noise is weighted towards the lower frequencies.
I’ve a feeling the static on TV is only black-and-white because the loss of proper signal on the colour channel will trigger the colour-mute circuit. You can see this happening sometimes with a weak TV signal - its may flip between noisy colour and noisy black and white as the colour-mute turns off and on.
Noise is everywhere. Higher pitch noise sounds like a spray-can hiss or, if you make it short, a hi-hat or cymbal. White noise sounds similar to untuned TV or FM radio noise (although truly random white noise is very difficult to make), and low frequency noise will sound more like the rumble of an earthquake or avalanche.