Speedometer Question

I have a 1964 Dart GT with the same problem, but mine also makes a crazy grinding/metallic sound sometimes too.(I now think it is the gauge)
I have taken the speedometer cable loose at the back of the speedo, pulled out the inner cable, cleaned it off, lubricated it, sprayed lubricant down the housing and it still doesn't help??? (I used speedometer cable lubricant for motorcycles)