I'm still trying out my new *ist DL and have noticed a strange mark off center on nearly all photos. I say nearly because the mark sometimes may be so soft it can be mistaken for image noise and can barely be seen. It seems to happen on any iso and two different lenses, flash or no flash. It is a cross 3x3 pixels at the 23.375" w and 13.875" position. I have attached a cropped sample of what I am seeing. Anyone know about this?