Ka-CHUNK! We all know the sound. If your derailleur is out of adjustment or you force a shift, your chain will let you know. Sometimes, it'll keep letting you know with a smaller ka-chunk every few pedal strokes. Usually, that means the bigger Ka-chunk damaged a link in your chain. A gouge or a burr near where two links meet can bind up the pivot. But a little carefully applied brute force can smooth it out. Find the offending link by listening for the ka-chunk and watching it pass through the derailleur pulleys. Fold the stiff link and flex the chain back and forth. Fold it the other way and repeat the process. What you're doing here is pressing the inner surfaces of the links against each other, flattening the burr, loosening the link and quieting your ride. Sometimes in especially rough Ka-Chunks, a link can twist, but we'll cover that next time.