Mine did the same thing until the needle finally broke off. I replaced my speedo with a different one and it works great.
If you want to keep yours and keep the milage accurate, here is how to remove it. Just under the dash pad is about 4 screws holding your instrument bezel in place. Remove those 4 screws, plus at least 2 screws from under the dash on bezel. Once the instrument cluster is loose, put down a towel or something to protect your steering column. Move the instrument cluster out towards steering wheel. Reach behind the instrument cluster and disconnect two large electrical plugs and the speedo cable. The instrument cluster should then just come out with some wiggling around the steering column.
Remove bezel then remove the speedo. I know there are people around that rebuild speedo's. They completely take apart and make like new. I would recommend that instead of pulling out and putting in a completely different unit.
Hope this helps.
Paul