What do you call that screen with the multi-colored bars on tv?

Question

it gives off a loud constant weird noise. the bars are multi-colored horizantal.

Answer 1

You may mean the SMPTE Color Bars, but those bars are vertical.

Answer 2

that is the emergency test screen. all stations would show it, if we were  under attack.

Answer 3

It's called a test screen.  In the old days it was on every night on each channel at the end of broadcasting for the day, until the next morning when broadcasting resumed.  I'm amazed you have even seen one these days.