Third one. Picked it up yesterday, bought four gigs of ram, did updates and now when I was installing the trackpad firmware update, I am seeing a sort of low visual "hum" not unlike a florescent light bulb before it starts to radically flicker and die. Are LED screens like florescents? I mean do they have alternating current flowing through them? If so, this is very very bad news. Artists will tell you never to use florescents because the underlying on/off current that lights up florescent tubes puts imperceptible strain on your eyes. I turned the brightness up and it seemed to stop. But if LED technology is anything like florescent tube lighting, this is going back and I'm getting a refurb. It will kill your eyes if you are looking at the screen for any amount of time. The other two did not have this slight visual hum, as far as I recall.