Originally Posted by
FBinNY
If it's a fairly new bike and the clicking happens once or twice per crank revolution, there's a good chance that it's simply the chain passing over the shift gate on the outer ring.
The shift gates are the cut down or missing teeth on the outer or middle rings (innermost rings don't have them). As the chain passes over them it can move over slightly then catch on the next tooth. It's comparable to the sound a train wheel makes going over a switch.
You can confirm this easily enough, by noting the crank position when it clicks, and then putting the crank in the same position and seeing if the gate is in the 11 o'clock position just about engaging the chain.
Tbh, I don't spend enough time on the train to know what that sounds like! It's always in the same pedal position, but like I say it's only when I pedal fairly gently. The bike's only a year and four months old and has done just over 1000 miles if it helps - is that something that shows something is wearing out? If so, what might be going? Apparently the chain is quite badly stretched, but it's expensive to get that changed.