Recently bought a new Colnago master that has about 700 miles on it, ultegra group. I had a clicking that I took the bike into a trusted mechanic to try to locate. apparently my pedals were not tightened down correctly when installed and that was what was clicking. However, the mechanic offered to clean the front chain ring and rear cogs, made them all pretty again as I had apparently been over lubing. He also elected to put a "clip" (not sure of what they are called) that allows me to remove my chain easily to clean it. Today was the first ride on it since the work done on it and now I am experiencing chain slip which I believe it on the rear cogs when I am exerting pressure on the middle and large chain rings. The mechanic has offered to make it right, but since this didn't do it before, could this be something as simple as a result of the "clip" changing the chain length (slip seems to occur from the center rear cogs to the lower ones on both middle and large chainring) or perhaps the cogs are loose???