What was found
FLT 994, DEN-BOS. DURING TAXI IN FLIGHT CREW AND CABIN CREW SMELLED ELECTRICAL/METALLIC ODOR. THIS WAS SHORTLY AFTER APU START UP. NO ABNORMAL INDICATIONS ASSOCIATED. ( AUXILIARY POWER UNIT (APU) SYSTEM ). FAULT ISOLATION PROCEDURES J21-22-00. INSPECTED APU COMPARTMENT . NO OILS/ FLUID FOUND . INSPECTED AIR CONDITIONING BAY AREA . NO OIL / FLUID NOTED . RAN APU FOR ALMOST 2 HRS . NO ODOR / ELECTRICAL FUME NOTED IN THE CABIN AND GALLEY AREAS . MDDR CLEARED . MX4 UPDATED PLACARD REMOVED . MCC NOTIFIED.