Mine get like that after while, its Verdigrease from your hands, strip it down and clean all inners.
What are you using as a mousing surface?
The Teflon feet on my Razer Diamondback keep it scrolling smooth - no fancy surface, just a free mouse mat I got with Supreme Commander![]()
Certainly sounds like something is wrong with it, am I correct in saying it's a wired mouse?