What was found
DURING DESCENT AT FL300, PITCH TRIM FLAG ACTIVATED. TCS'D & TRIED PITCH WHEEL MANUAL DOWN, JAMMED. TRIED ELECT TRIM & DID NOT WORK. RELEASED TCS & REENGAGED AUTOPILOT & DISENGAGED AGAIN & TRIED PITCH UP ELECT PITCH & TRIM WHEEL STARTED TO MOVE. TRIED MANUAL WHEEL & NOT JAMMED. OK UNTIL ABOUT 3 MILES FROM FINAL W/ AUTOPILOT OFF, & USED ELECT TRIM DWN & TRIM WHEEL MADE A LOUD POPPING, BUT SEEMED TO WORK NORMAL. CLEANED & LUBED TRIM TAB ACT SYS IAW MM 12-20-27, MULTIPLE TIMES OPERATION TRIM TAB CHECK GOOD, VERIFED TRAVELS & CABLE TENSION CHECKS OF ELEVATOR TRIM, NO DEFECTS . INSPECTED PULLEY , TURNBUCKELS & ROUTING CABLES, NO DEFECTS. COMPLIED AUTOPILOT SYS OPS & ADJUST TEST, COULD NOT DUPLICATE.