Speedometer cable is the term. Yes, it turns inside its casing and
eventually needs some lubrication with very light oil, but consider that
the speedometer itself may be the source of the noise since it has
rotating parts too. A speedometer cable in need of lubrication often
makes the speedometer needle jerk up and down as the cable sticks and
releases, sticks and releases. You don't comment on that so the
speedometer itself may be the problem.
If you can't get to the cable by reaching up to it from behind the dash
then removing the instrument cluster is the alternative.