:hate: My chain will hop occassionally no matter what rear cog it's on. It doesn't happen every revolution of the cranks, either. It will run smoothly for 2-3 revolutions, then rise up as if it wants to go to the next bigger cog, or as if it's not seating on the current cog. Also, the pulley arms will jump a little. I've fiddled with the screws on the derailler, and it runs from cog to cog alright when I switch gears. I've tightened and slackened the derailler cable; it doesn't seem to matter much. Could it be the chain or pulleys? I've adjusted deraillers on other bikes, but this one is giving me troubles (Trek 1000c).