Several times per ride, usually from a stopped or slow speed, the drive train skips with a sort of clanking sound. Ultegra 10 speed cassette 3 years old, new Ultegra chain, DA rear derailleur. It is NOT jumping cogs I know that. It clanks and stays on the same cog. I can never see what it is in time or reproduce it on the stand. Drivetrain is clean and well adjusted (unlike me). Could it be a tight link? I can't find any. WTF?!?!?