My XT 11 speed rear mech has suddenly developed an odd noise from the lower rear jockey wheel when in the lowest gears. It’s not the normal squeak from the jockey wheel itself, but seems to be caused by the small lateral movement of the rollers across the jockey wheel as the chain feeds on at an angle. The problem started quite suddenly, so I’m wondering if it’s had a bash, but the hanger is straight, and everything else looks and works fine. The jockey wheel itself seems fine and spins very freely.

Bearings or bushes (I’m not near MrsF’s XT mech at the moment.

I’d pop the jockey off and clean/regrease both systems.

Bearing could be worn, or indeed the bushing !

I always apply grease to my road bushed jockeys, even when they are ceramic.

Pretty sure it’s bushes, although it spins remarkably freely.

I’ve had squeaky Shimano jockey wheels before, but this noise doesn’t seem to be the jockey wheel itself, but rubbing between the chain and jockey wheel.

Nope, bearings.

Well that’d explain why my one spins so freely 🙂

Hanger is straight

Looks straight, or is straight? Doesn’t take much to upset 11 speed. Would explain the sudden onset.

Does it have a clutch?  Could be that the clutch is sticking and the derailleur isn’t moving properly, esp if it came on suddenly…