I first have to explain I looked through the forums and could not find my issue and some that were close to mine are kinda old forums post. When my wife is playing Farmville or one of us watches something on Youtube fullscreen it starts flickering non stop. I can see the white lines on it. This only happens when we click on a button to make it full screen. I even tried different browsers and the same issue happens. Not sure what it is. Should I back up and format my hard drive and reinstall Snow Leopard? I hope it's not a motherboard issue.