As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING DECENT FL260 AT 300KIAS, NOTICED A BACK & FORTH FLUXUATION ON TRIANGLULAR RUDDER TRIM INDICATOR, FOLLOWED BY AUTOPILOT KICKING OFF WITH AUDIBLE ALARM. RESET AUTOPILOT & IT KICKED OFF 1 SECOND LATER. APPLIED SLIGHT PRESSURE TO RUDDER PEDALS & FELT A "THUNK" WHEN DEFLECTING. NO MOISTURE VISABLE, UNUSUAL NOISES OR BINDING ON POSTFLIGHT. REMOVED & REPLACED NR 1 AHRS. ATTITUDE AND HEADING CHECKED GOOD. HEADING SWING ACCURACY CHECKED GOOD. WORK PERFORMED IAW MM 34-21-01.