So its definately the cable then... not the string. That makes it easier.... if the serving is worn, then there has been a change in the overall diameter of the serving... smaller serving makes it easier to slide up the side wall of the roller and then snap back down to the bottom. There are a couple ways to fix this.... first... you probably have some cam lean anyway... to fix that, you are going to have to twist up one side of the yoke on your cable.... that will probably fix the problem. You could also have your cable reserved.... or if it has been a while... even replaced altogether.