I was taking my bike around the block today, just to check everything out before packing it up, and I noticed that when I accelerate, the chain rattles and shakes. When I look down at it, it's making a fast clank clank clank sound, and not running true. When I back off the gas, it runs perfect true, not wobbling or rattling. The sprockets look fine. Not pointed, none are broken.. Sprockets are tightened fine.. Any ideas??