A projection display system may be mechanically perturbed to remove or reduce speckle. In addition, pixellation effects may also be removed or reduced. By mechanically disturbing a portion of the system, for example using a wobble perturbation, the speckle effects may be temporally smeared so that they become invisible to the user. In one embodiment of the present invention, a folding mirror may be mechanically perturbed, using a plurality of piezoelectric actuators, at frequencies in the ultrasonic range.