Overheating mouse..

I have a problem with a mouse getting rather hot, literally. It does not get hot enough to burn much hot enough to make it defficult to hold the mouse. I have tried both ps2 and usb versions and have the same problem. The problem is also intermittent and does not seem to relate to any one event. My only thought is that there is a voltage regulation problem on the motherboard(Asus me99vm), but how would I check this?
Any other ideas??