Yeah, I hate it when a bike starts making an unexpected noise, but I also know to stop and check things out. With all my trail riding, I pick up a lot of leaves and twigs and mud - all sorts of stuff. Interestingly, in all my years of riding in the snow and cold, though, I've never once had a derailleur or shifter freeze on me. That was never the problem on my winter commuting days. It was that darn salt they used on all those Chicago streets and that stuff would eat up everything on a bike. That's where the daily cleaning and sometimes a shower would come in.