We have been there many times. Since I have no idea where you would get parts (unless you want me to send them), I think you can do the job yourself.
Remove the inst cluster. Remove the speedo from the cluster. Remove the back metal plate from the speedo. The speed cup drive will be seen. The input shaft has the magnet built to it and is assembled into a housing that can be removed with two screws. There is an end play adjusting plastic bushing that has a small lock nut and shaft adjustment. The noise comes from the heavier magnet end of the shaft dancing within the freeplay. The solution is usually a new housing which carries the shaft supporting bushing. The answer without parts is to clean every thing and lube with a light grease (small amount) and then adjust that end play till there is none. DO NOT MAKE IT TIGHT. No end play but NO preload. This will probably solve your problem for a while. If the bushing in the housing is too worn it will wind up with end play again in a short time.
Bosch Master, ASE Master, L1
33 years MB technician