Canon 18-135mm EF-S IS lens shakes when focusing

My Canon 18-135mm lens shakes whenever I try to rotate the focusing ring. The Canon 60D is sturdy on a chair (sorry no tripod yet) and the only thing that I am moving is the rotating ring so I am sure that it is not the camera that is being moved when focusing... The focusing ring is being rotated back and forth and the lens somewhat shakes from the inside. Stabilizer switch is in ON Position. Picture wise its not a problem at all, but video wise, it might affect the video since the lens shakes whenever I use the focus ring... Is this normal or is my lens already showing signs of any issues?