I have a newly installed campy 10 speed double drivetrain with bar-end shifters. With the chain shifted to the smallest cog in the cassette the chain jumps, for lack of a better word. This isn't ghost shifting or bad trimming. The chain actually jumps vertically a little bit ever revolution or so, though speed and force seem to play a part. The rest of the shifting is as smooth as can be, and both the front and rear derailleur seem to be setup perfectlly except for this weird "jump." Has anyone encountered anything like this, or fixed it?