It does it worse when its warm or the car is warm? If so sound like you could have a potential short somewhere. Check the speed sensor on the trans, it could have a wire that touched the exhuast or gets up against the exhaust when moving.
I might have found the problem. I think it has something to do with the saleen over lay.
It is a saleen mustang. I think what is happening is when the heat gets to the cluster, the glue might be coming apart. So I took it apart and pulled the needle out just a little bit more.
So we'll see. Calling for rain so it is going to sit for a while. lol