What was found
FLIGHT ATTENDANT IN AFT GALLEY REPORTED DIRTY SOCK SMELL AS AIRCRAFT PULLED INTO GATE. APU WAS RUNNING, APU BLEED OFF, ENG #1 WAS RUNNING, ENG #2 SHUTDOWN. APU HAD ONLY BEEN RUNNING ABOUT 4 MINUTES. AIRCRAFT WAS GROUNDED DUE TO DISCREPANCY. MX PERFORMED OPS RUN OF ENGINE #1 AND #2 AT GATE WITH PACKS ON/OFF. COULD NOT CLEARLY IDENTIFY ANY TYPE OF ODOR, PER EA # A0-21T-34386. PERFORMED TROUBLESHOOTING PER TSM 05-50-00-810-831-A, POSSIBLE SOURCE IDENTIFIED AS TYPE 9, MISCELLANEOUS, NO ABNORMAL SMELLS IDENTIFIED. OK TO CONTINUE.