I have about 4000 miles on my ST1. I pedal hard in city mode @30% about 22-26 mph. Recently I developed some knocking sounds coming from the rear I believe. If I go up to Tour or Power mode the knocking is more frequent and louder. I can wobble the cassette a mm or two with my fingers, I don't know if this is by design, or something wrong. Anyway, without working on it in the cold garage, what is the back end made of, freewheel or hub? Is there a way I can fix this with a little grease, or do I bring it in to the LBS. Please advise friends. Thanks.