I noticed that the driver side front quarter panel rubs on the A pillar and on the other side is spaced properly. After loosening the screws holding the quarter panel down, i pulled it out a little and now it doesn't touch anymore. Took it in to service department and they are going to repaint the area. The bozo who programmed the machine that puts these panels together must have screwed up on the spacing. At the dealer, every 2013 mustang
had the same problem.