My left brake-shifter lever was chattering over rough pavement. I checked it out and found that the main lever (SRAM) was slack due to the brake pivot bolt sticking. The brake return spring was not pulling the lever taut. A little WD40 on the pivot bolt fixed it right up. Been experiencing some hard riding when everything should be normal. Probably due to the same cause, the brake pad not returning and dragging on the rim.