Just putting a rear mech on my Explosif SS for an upcoming big ride - just flicking through the gears and finding that the [new KMC] chain is riding up on the 11T sprocket every couple of links (no other sprockets involved) until the chain is sitting on top of the teeth, then plopping down into the teeth. I bought a new chain because this also happened on my old {slightly worn SRAM] chain and thought it was a wear issue. Both chains are 8spd, as is the Shimano block. Rear mech is an old XTR, and never had problems with it in the past. Front ring is a 32T Surly SS.
I have replaced the 11T with another one laying around.
It doesn't skip on the neighbouring 12T, and all other sprockets are fine.
I have slid the dropouts forward, backward and all points in between in case it was a 'chainstay' length issue.
The teeth aren't broken, the chain is perfect.
The mech cage distance adjuster screw is set to max.
The only thing I can think of is a nackered top jockey wheel which is goosing up the chain being fed to the 11T sprocket...
Any suggestions appreciated.

