Hmm, that's another possibility. I'm waiting for delivery of a chain alignment tool...gizmo that clamps to the rear sprocket and runs a straight rod along the top chain run..... presumably if I do this at different points on the rear sprocket any run out would show up.
What makes cush rubbers my no1 suspect is that when the tyres were being fitted I glimpsed one of the' techicians' with a handful of cush rubbers.....I recall thinking that I didn't seem to remember needing to remove these last time I took out the wheel myself.
