Usually it's a dry cable, but also can be the driven gear in the trans.
You can pull the cable loose from the trans where it connects to the speedo assembly and semi gently pull the center cable out of the housing so you can lube it.
Lube it with white grease or a dry lube like graphite (both work really well) as it goes back in and a little twist at the end to seat it back into the speedo.
I know it's extra work, but I took off both ends and poured oil in the top until it came out the bottom. That's quieted mine for over a decade. Works on motorcycles, atvs, and sleds too.