Join Date: Jul 2005
Location: St. Paul, MN
Bikes: Cannondale CAAD9, Ritchey Breakaway Cross, Nashbar X-frame bike.
Mentioned: 2 Post(s)
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Quoted: 118 Post(s)
Which gears is it doing this? By "moving mechanism" I assume you mean the cage which the chain runs through?
If you are aggressively cross geared (biggest front to biggest rear, or smallest front to smallest rear) sometimes that just happens, and there's nothing to be done about it. You shouldn't be riding around cross geared like that anyway. Use your other chainrings to straighten your chainline.
If it's rubbing in straight chainline scenarios, the problem may be as simple as your limit adjustment screws. You can learn to adjust those yourself easily in a few moments...or I'm certain your LBS would hook you up for free if you're a good customer. It's an easy tweak.
Good night...and good luck