Assuming it's not the Ujoint (which should go completely out any time if it is going bad, so don't go too far) (with a lot of clunking and grinding), it's very likely the dampner rubbers in the rear wheel assembly. Easy on goosing the throttle (or dropping the clutch) in the meantime.
Regardless of miles, rubber does not last forever (or 21 years), so order a set of those right away. There used to be two sets: one for standards (2-piece) and one for interstates (1-piece), but only the 1-piece are available anymore (with the inserts already installed in them), which was always a better design (and fit all years and models of Valkyries).
Number 1 in this fishe:
https://www.procaliber.com/oem-parts?aribrand=HOM&arian=MOTORCYCLE#/Honda_Powersports/GL1500CFA_(99)_VALKYRIE_INTERSTATE%2c_USA%2c_VIN%23_1HFSC410-XA000001/REAR_WHEEL/61347acc-638e-40e4-aa4f-0fceb839ab88/b81dc208-929f-4689-a4c9-7ed0d5035d35/y
They only go in one way. If you put them in upside down, the cover plate won't seat properly.
You might also want to order a spare thrust washer (#4) since they often go missing (or forgotten), and are important to the life of the rear drive.