As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RUDDER SHAKES INFLIGHT INTERMITTENTLY FROM FL410 DOWN UNTIL AC SLOWED TO 250KTS. FEELS LIKE LIGHT TURBULENCE. THIS WAS THE STRONGEST WE FELT THE SHAKE WHILE DESCENDING. TROUBLESHOT RUDDER TRIM SYS; FOUND FWD LOWER RUDDER TRIM ROD TO HAVE EXCESSIVE PLAY. INSTALLED NEW ROD PN 4A55820111-03 AND BOLT PN NA567040V12 IAW MM 55-40-10.