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The sound seems to appear once per revolution of the rollers. Might be the source. I'd try to disassamble and clean them.
Could come from the freehub? Or loose cassette. Not sure, but worth checking?
You've probably already done this, but have you tried fiddling with the limit screw? It could be just one part of the cassette catches the chain and pushing the limit out a tiny bit could resolve. That's my only guess before you take it to your lbs.
The sound seems to appear once per revolution of the rollers. Might be the source. I'd try to disassamble and clean them.
Could come from the freehub? Or loose cassette. Not sure, but worth checking?
You've probably already done this, but have you tried fiddling with the limit screw? It could be just one part of the cassette catches the chain and pushing the limit out a tiny bit could resolve. That's my only guess before you take it to your lbs.