The rear cassette shouldn't be too worn. I bought the bike new last August and rode my other bikes through the winter. I have also been pretty good about cleaning and lubing the chain, and I replaced the chain well before the "chain checker" tool showed much wear. I'll check the rear derailleur adjustments and make sure everything there is good and then hope it goes away or at least doesn't get any worse. Otherwise I'll bring ask the LBS next time I'm in there.