1. While riding the bicycle, a continuous metal clashing sound occurred. When I stopped and manually spun the chain, I could reproduce the issue. See Video 1.
2. Upon closer inspection, I found that the cause should be a slipped chain. See Figure 2.
3. First, I manually re-seated the chain onto the sprocket, then spun the chain so it would fully seat itself automatically.
4. The problem was then resolved, and the sound stopped.
5. I found that it was still not completely resolved. I finally decided to take it to a bicycle repair shop, and they ultimately discovered that the root cause lay in the bottom bracket—some of the bearings inside the bottom bracket had corroded. See Figure 3.
6. After replacing the bottom bracket, the new one uses the same technology as shared bicycles, which differs from the old bottom bracket technology; the old bottom bracket contained some steel balls inside. The problem is now completely resolved. See Figure 4.
