Originally Posted by FBinNY

Stupid question. Is it possible you're hearing chain noise?

Depending on the chain lube you're using, and it's condition, is might simply be a matter of lubing the chain, and certainly you should eliminate that possibility before taking things apart.

Also note the crank position when you hear the loud "clack", duplicate it and examine the teeth just about to engage the chain at that point. If it's at the shift gate, or there's a chipped tooth, that's might be making the noise as it engages the taught chain.

After eliminating the simple possibilities, you can explore more complicated ones. If you approach the problem from the opposite direction, you could end up unnecessarily doing complicated, expensive and pointless work.