Seems there's more than one model with this issue and it also seems Samsung is having the same problem. Check out the following forum:
Anyone have any ideas as to why the blank screen would resemble clouds or more accurately muddy, rather faint, light and dark areas that resembles smoke? It also appears when watching a DVD in the letter box and into the picture. It's consistent whether watching TV or DVD and always in the same area, the shape and size of the "smoke" is always the same and in the same place. It's only noticable in darker conditions and dark scenes. Just bought it, using HDMI cables to connect cable box to TV. Had a Samsung 40" LCD that I returned that did not have this problem and it was hooked up the same way.
Thanks for any help. HD... what a difference.