No ideas Hooky, but I just thought I would share this with you. I bought Packard Bell optical mouse. And it has always felt the urge to quickly visit the bottom of the screen on the odd occasion. Then it is normal again in a split second. As I run three monitors, with the taskbar on the left handside monitor, it just does a quick "exit stage left". I have never found what is causing it, but itis no sweat.