Some dock icons displaying a vibrating look-how to fix?

The 'vibrating' look on some of the dock icons (both Apple ones and other software ones) doesn't seem to want to correct itself, whether I do a repair permissions or not.

Any assistance to bringing the icons back to their normal in-registration look would be greatly appreciated.

This has only been going on now for about a month. Currently I have Snow Leopard 10.6.8 installed.

Thanks in advance....