They're using HTML5 Canvas to create that noise animation, its drawn with Javascript rather than CSS which is why you wouldn't be able to work it out from inspecting it.
Here's a tutorial on how to create static/noise textures:
http://code.tutsplus.com/tutorials/how-to-generate-noise-with-canvas--net-16556
And here's a demo:
http://jsfiddle.net/AbdiasSoftware/vX7NK/
I believe this part of the code is creating the random static:
buffer32[i++] = ((255 * Math.random())|0) << 24;
Might be worth also watching some intros to HTML5 Canvas too like this:
https://www.youtube.com/watch?v=VS1mD9Z0h-Q