I have just bought the cannon 40d and sigma 18-200mm lens,and the cannon 400 f5/6 prime lens,when I fix a lens to the camera,they lock,but if I twist the hte camera one way and the lens the other,their is a slight play and clicking sound between lens and camera.it is only slight,and when walking with it in my hand,their is no movement or noise,like the lens is lose,and the pictures are ok.as any one else found this with their camera,is this the norm.thanks.