Kensington Mouse "Drifting" Problem/Suggestions for Replacement

I've owned a Kensington 3-button Optical Pilotmouse for about 1.5 years now, and after about 4 months the mouse started to "drift" on its own. It was not my touchpad that was the problem, because it stopped happening when I unplugged the mouse, and it occured when using the mouse on other systems as well. At first, the problem was just a nuissance as it only occured from time to time, and only slightly affected pointing precision; however, it got progressively worse and after a year the mouse was completely useless.

Last month, I informed Kensington and they honoured their 5-year warranty by replacing it with the current equivalent model, the Ci20 5-button mouse. I enjoyed using the mouse for the first couple of weeks, but it didn't take long for it to develop the same problem as my first Pilotmouse.

Has anybody else experienced this problem with either of these Kensington, or any optical mouse for that matter? I never experienced this problem with my basic Microsoft optical mouse. While I could take the matter to Kensington again, it seems somewhat pointless seeing as how the replacement mouse they sent me is plagued with the same problem as the one I originally bought. I'm not too choked about it since I paid under $10 for the original mouse.

I will most likely replace it something like a Microsoft IntelliMouse Explorer 3.0 "gaming" mouse.

 

See if the optical lens is being diffused by lint or dust. I know if the hole where my mouse's laser sensor is has something in it--it can behave like that.