904 '73 Duster, has a new cable in it. I thought I greased it, not sure. it bounces around, holds steady at the wrong but close speed and then bounces around, if you listen you'll hear a tingy or ringing sound from it..What could that be?

My speedo did this on my GTX and it turned out that the speedo cable wasn't fully installed on the back of the speedometer.

I had my barracuda speedo rebuilt at a local speedo shop because of the same issue. They said that bushings inside let the rotating parts wobble and come into contact with each other and make that tingy noise. It was smooth as butter after the rebuild. I actually had one speedo that broke the needle off because of the bouncing.
Travis..

It pays to look at all the parts to the puzzle. The speedometer itself can be failing. The cable at the speedo could be loose. The lube in the cable may have dried out. The rotating cable inside may have frayed. The cable screw cap at the trans could be loose or on crooked. The speedo pinion may be out of adjustment. Finally, the pinion may have one or more teeth chipped.

I agree with all of the Frankenduster. My Cuda speedometer was bouncing, turned out the cable was dried out. I cleaned and lubed it, it's been fine since.

lub the cable

Also make sure you have no sharp bends in the cable--especially behind the speedo itself. The cables operate a LOT smoother when they are straight as possible. On some cars thats not easy

The tingy sound is the key. That usually means the bushings in the speedo are worn and the rotating parts are touching. Squealing can be the cable.