I have a 3 months-old mid-2011 27" iMac which recently (I don't know when it exactly started) has build a long-painful to look at- streak/smudge mark behind the LCD. Obviously not on the glass surface, it's on or behind the LCD. Looks annoying when the color is light, but overtime I see it become gradually a bit thicker as if it's dust built by fan (or is it?) I realize there are some threads discussing this already. But since I need to know your opinion more well, I made a new thread instead, sorry So .. how about your iMac, does it build up a smudge mark on the LCD? For how long do you have the iMac? Will Apple take care of my iMac if I take it in? Do all iMac has this problem over time? What will AASP do then? Replace the LCD? Or can it be simply cleaned and prevented for future build-up? The LCD itself is fine, no dead pixel, yellowing or anything but the smudge marks. But no-less annoying since I can notice it easily. It's on the screen, man Will it come back again after several months? What's the source of the problem actually? I thought the panel and backlight was sealed from fan and machine behind it?