As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT, PASSING THROUGH FL300, FELT A/C TAIL OSCILLATING RAPIDLY L/R. OBSERVED UPPER RUDDER CARAT ON FLT CTL PAGE MOVING RAPIDLY L/R WITH ABT .2500 OF ITS DISPLACEMENT. REMOVED AND REPLACED "B" CHANNEL YSAC IAW MM 27-24-01. OPERATIONAL CHECKS GOOD.