What was found
(CAN) FLIGHT CREW REPORTED DURING CLIMBOUT AT 280 KTS, THE RUDDER STARTED TO OSCILLATE RT AND LT. AUTO PILOT WAS IMMEDIATELY DISCONNECTED. OSCILLATION CONTINUED LT AND RT. YDNR 1 INOPERATIVE STATUS, MSG APPEARED. TRIED TO DISCONNECT YD NR 2 BUT WOULD NOT DISCONNECT. SLOWED TO 200 KTS AND WAS ABLE TO DISCONNECT YD NR 2 BUT OSCILLATIONS LT TO RT CONTINUED. LANDED 100 LBS OVERWEIGHT WITHIN THE 300 FT/MIN LIMITS. YD LINEAR ACTUATOR NR 2 R & R. A CHECK FLIGHT WAS PERFROMED WITH NO FURTHER DEFECTS NOTED. ACFT RETURNED TO SERVICE. PART NAME: ACTUATOR PN: 622-9968-001.