Digital darkness

Create a new document of any size, for this example l will create a document that is 1024x778 - for a standard desktop background. Fill the background with black (#000000).

Create a new layer. Get out the rectangular marquee tool, and make a selection like so near the bottom left corner (region) of the canvas:







Fill this selection with the paint bucket using the color #4a4a4a.









Press CTRL + D on your keyboard to deselect the selection. And go to Filter->Distort->Wave and apply the following settings:





Tip:

Click the 'randomize' button until you get an "random" result, avoid a pattern look.



Result: