What was found
DURING DESCENT , FLIGHT ATTENDANTS REPORTED ORORS CONCENTRATED IN THE AFT PART OF CABIN. THE FLIGHT CREW TURNED OFF PACK NR 2 THEN FA'S REPORTED THE ODOR GREATLY IMPROVED. AFTER LANDING, APU BLEED WAS USED WITH PACK NR 1 ONLY. THE FA'S THEN REPORTED THE FUMES OF UNKNOWN ORIGIN RETURNED TO THE AFT CABIN. TROUBKESHOOTING CARRIED OUT IAW TSM 05-50-00-810-831-A. VISUAL INSPECTION CARRIED OUT ON BOTH ENGS AND APU. NR 1 AND 2 ENGINES GROUND RUN AT IDLE BY CREW WITH PACK OPERATED ALTERNATELY. UNABLE TO DUPLICATE CABIN FUMES. OK FOR CONTINUED SERVICE.