I just received a new 27" iMac late 2013 and on the very left hand side of the screen is a faint thin grey bar or line. It isn't so much of a problem because my eyes rarely look at the very left of the screen. It is however strange because it starts at the very top left from the absolute corner, it then curves in by 2 or 3 mm and then drops straight down in a straight line which is only 1 maybe 1.5mm thick until about half way down the screen when it just disappears. It is hard to photograph, it is quite faint but almost looks like a shadow. The thing that threw me is the curved/diagonal from corner bit at the top, so i don't think it's a pixel issue. As this is a replacement for an iMac with a crackling sound, it is perfect in every other way. Could this be a screen defect or a dirty mark under the glass?