How do they make that effect?

I realy like this effect you see on the link i have below. The one on the main graphic with the lines randomly going back and forth. I have see it on numerous sites but i have no idea how to do that. If anyone can point me towards a tutorial or give me some advice on how to do it, i would realy apreciate it. thanks again guys.

thanks dudeā€¦i apreciate it!