I have recently noticed that my speedometer needle sometimes twitches upward from zero when the car is not moving with the engine running (as in, while sitting at a red light) It doesn't move much, maybe 1/4", then drops back down immediately. Sometimes it will do it more than once, at random intervals. I don't think it it used to do this, though I've only had the car for a few months. When moving, the speedometer seems to be working normally, though the odometer is dead.

Any ideas why it does this?

Is it likely to get worse, as in, jump around wildly all the time?

Should I start looking for a replacement? (hopefully, a cluster with a tach)