Did a long gravel ride at weekend and near the end when in lowest 4 or 5 gears (big cogs) there was a noise like a dry bearing rumble soon as went into bigger gears disappeared.
i cleaned, degreased chain and derailleurs and re lubed. However same noise. What is strange is that it starts around 4 or 5 from biggest sprocket, if go up one more and then drop it back to original rumbling gear the sound disappears?

i have a giant revolt with GRX x 1 with a 11-42 rear.

Anyone have any experience thoughts or ideas before i start taking it all apart and probably failing to fins the cause?

If it’s disappearing when you shift back in the opposite direction, it suggests something’s not lining up in the same place twice. My guesses would either be a sticking cable/ mech, or something slightly loose that’s allowing a small amount of movement, maybe loose axle, mech or cassette, or possibly worn freehub bearings.Edit: also check your B tension/jockey clearance/mech hanger alignment first.

I had similar (and many other problems) with a sram rival mech just before it disintegrated due to jockey wheel bolt undoing itself.

Problem solved when rebuilt with added blob of locktite.

Its the clutch on the derailleur. Noise only there when it is on and also much harder to change gears. Anyone know if something can be done?