If it is making noise, then it is the cable. Speedo heads don't make noises unless they are self destructing, and yes I've had that happen. You just need to work on the cable to get it loose. It is only held in by the threaded ferrule.
Speedo heads can be cleaned and rejeweled by almost any speedo shop. If the permanent magnets need replacing, they will do that too. They can recalibrate it quite easily also.
After doing all this, the can check to make sure that your speedometer is reading correctly when it is reinstalled in your car. Sometimes people swap in different speedo gears/rear gears/etc., so it is nice to have a speedo you know works correctly with your car.
