I've got some strange, dark lines on the glass of my iPhone 6. (not a pixel issue.) 4-5 wide vertical ones across the whole length of the device and two short thin horizontal lines in the middle of the device. The lines are parallel and perpendicular with each other, but a few degrees off from the shape of the phone itself. The lines are most clearly visible when the phone is off or with the brightness turned down low outside or under a bright light. I did not notice them immediately on unboxing because they are almost invisible when the phone is wiped clean. In fact when I first cleaned the glass I thought I had gotten rid of them. They only become apparent after finger smudges build up on the glass through use. Does anyone have any theories as to what could cause a defect like this? I've searched to see if anyone else has had similar issues with no results. I've got a genius appointment tomorrow. Any ideas?