Speedo Cable
Timbolia,
I don't know about the noise, but the first thing that I would check as far as being "off" is the speedometer pinion gear. There are different pinion gears required based upon rear end gears and tire size. I don't have access to the thread off the top of my head, but the subject was discussed on this site in the past. You can also try an internet search for the formula if you can't find the thread.
BlindSquirrel