I recently received some C-41 120 negatives and prints from a lab I've used in the past with satisfaction. While the prints are fine, the last two or three negatives display, on the base side, some regularly spaced marks. These marks didn't show on the lab's prints, but they are really evident on scans I made with my Epson V700. The film was Fuji 400 speed, I used a Pentax 645n, if that info makes any difference. Film cleaner won't remove them, an email to the lab hasn't been answered. Any ideas?