Mystery Bike Noise Finally Solved

by Chikashi

For the last few weeks I have been hearing an unfamiliar and annoying noise when I pedalled. It sounded like a bare, taut cable being plucked, similar to a muted note on a string instrument. Usually, these bike noises tend to have a regular pattern, namely, once a revolution either of the drive train or the wheels. This one was irregular. Sometimes it was once a revolution, sometimes it was twice a revolution but not at equal intervals. All I knew was that the noise is audible only when I pedalled, not when I coasted.

I tried to identify the cause on several occasions, but I was not able to spot it because I was unable to replicate the noise on the repair stand. I realised that the noise occurred only when there was resistance on the rear wheel / drive train, so I thought of putting the bike on the turbo trainer to see if the noise becomes audible. However, I never got round to it, not for any good reason.

On the way to the start of a club ride the other evening, my chain got stuck in the rear derailleur. It got unstuck fairly easily, and the drive train seemed to be working fine again. Therefore, I went along with the others on the ride, which featured one of the boys hitting the deck at 40+ kph during a group sprint.

Yesterday, whilst wiping down the bike, I remembered the chain getting stuck and had a closer look at the rear derailleur. I was able to replicate the problem, and this is when I found the likely cause of the plucking noise. One plate of an inner link was broken in two pieces.

I never had a broken chain before, so this was an interesting discovery. I always wondered about the durability of these 11-speed chains with paper-thin plates. I have done a bit more than 6000 km with the chain, and one mechanic at my LBS told me today that an 11-speed chain should be changed every 2000 to 3000 km.

That recommendation may sound a bit exaggerated, but I am inclined to think that it is better to be safe than sorry. If the other plate of the link broke during the group sprint the other evening, it probably would have resulted in a much bloodier scene.

I shall pay more attention to the condition of the chain from now on.

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