1992 Passat Jumpy Speedometer

Lately my speedometer has started to jump around randomly. Sometimes it is when you first start out after being stopped, and others it will just randomly start to jump all over the place. After a little while of this acting up, things go back to normal and the speedometer reads fine until the car stops again. Any help into this problem would be greatly appreciated. The car has a 2.0 16 V with a 5-speed tranny.

Cheers