It's your cable tension....shift it into the smallest cog in the rear, wind out the barrell adjuster to let some slack in the cable, undo the cable anchor bolt,then pull the cable reasonably tight with your fingers !! ,do up the anchor bolt nice and tight,move your STI ****er into the next gear up from the smallest, then spin the cranks(assuming you are using a workshop stand) with one hand while turning the barrell adjuster with the other ..keep turning the adjuster untill it shifts into that next gear you put your shifter into..fine tune untill it's as quiet as it's gonna get...then go up and down the gears with the shifter to check it's all moving smoothly...cheers and have fun...
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Velosophy#1: It is better to have a bicycle and no money , than money and no bicycle ! Velosophy # 2 : "Winning is simple, but not easy." #3: "Give a man a fish and he shall eat for a day , teach him how to fish and he will sit in a boat and drink beer all day"