As title says the XX1 rear mech has developed a knocking noise that can be felt through the frame, I had a similar experience with a older OX type 2 mech, SRAM tech tell me I can send it back but I was hoping some one might be able to shed some light on it & if there is a fix I can do.

Cheers

i have a zee mech that does the same. the clunk is coming from the clutch. It’s better when it’s not engaged, but not eliminated.

XX1 Type 2.1 mechs are officially non user-serviceable. There was a bodge fix – adjusting the strength of the clutch – knocking around the inter webs a while ago but it only applied to Type 2.