I'm stumped. I'm running a Tiagra 4503 crank, HG53 chain and cassette. Chain and cassette have 2000-3000 miles. Crank is pushing 13000 miles. Cassette is a 12-23 9-spd.
When I'm in the big chainring-central cog combination, I get quite a bit of popping and roughness. For those that have had a chain break slowly, it almost feels as if one of the plates in the chain is about to pop off, or that maybe I have a stiff link, but upon inspection all looks fine, and in any other gear combination, all feels smooth.
It's gotten progressively more noticeable over the past few rides, and seemed to get worse when I relubed my chain.
I do spend the majority of my time riding in that gear combination.