The correct answer is C) cleaning the collector rings with a canvas wiper. Chattering of the collector/slip ring brushes on a generator is often caused by buildup of carbon and dirt on the collector rings. Cleaning the collector rings with a canvas wiper can help remove this buildup and smooth the surface, which will resolve the chattering issue. This is a common maintenance procedure recommended by generator manufacturers and Coast Guard regulations. The other options are not the best solutions for this specific problem. Lubricating the brush holders (A) may temporarily reduce the chattering, but it does not address the root cause. Re-insulating the brushes (B) is not necessary, and increasing the length of the pigtail (D) would not resolve the chattering.