When riding this weekend I had something strange happen. while running on pavement or hard gravel and getting on it pretty hard, I'd get a skip in the driveline that felt like a chain jumping a tooth on the sprocket in 3rd and 4th. Didn't happen all the time and it would only be 1 quick jump. I stopped a few times and checked my chain, it was not loose. My front sprocket is new (first ride) and the rear has about 20 hours on it. Suggestions?