What was found
ELEVATOR TRIM AUDIO (CLACKER) BEGINS RUNNING CONTINUOUSLY DURING FLIGHT WITH AUTOPILOT ON BUT NO TRIMMING ACTUALLY OCCURS. THIS ONLY HAPPENS WHEN FLIGHT GUIDANCE (B) IS SELECTED AND THE AUDIO STOPPED WHEN FLIGHT GUIDANCE TO (A). THIS HAS OCCURRED DURING CRUISE AT HIGH ALTITUDE AND ALSO AT LOW ALTITUDE DURING APPROACH. CONNECTED EXTERNAL POWER. BROUGHT UP AVIONICS SYSTEM "CLACKER" OPS CHECKS GOOD. RAN AUTOPILOT AT INTERVALS OVER A 2 HR PERIOD. COULD NOT DUPLICATE.