What was found
AT APPROX 2030, PILOT REPORTED, DURING THE INITIAL TAKEOFF, HE & CREW BRIEFLY HEARD AN UNUSUAL HUMMING SOUND. ELECTED TO CONTINUE THE FLT AT THAT TIME. SEVERAL MINS INTO FLIGHT, CREW REPORTED AN UNKNOWN ODOR IN AFT CABIN. PILOT DECIDED TO MAKE A PRECAUTIONARY LANDING & CONTACT MAINT. ON ARRIVAL, MAINT REMOVED TRANSMISSION COWLINGS & INSPECTED MGB AREA, ALONG WITH BOTH ENGINES. THE ONLY DISCREPANCY NOTED WAS RT ENG SUMP CAN & ASSOCIATED LINES WERE FULL. IT APPEARED THAT UNUSED OIL & FUEL MIXTURE HAD VENTED THROUGH VENTURI INTO EXHAUST, LEAVING A WET RESIDUE. BELIEVED TO BE SOURCE OF ODOR. FURTHER INSP FOUND ONE DRAIN LINES TO SUMP RESTRICTED, & VENTURI IN EXHAUST EJECTOR HAD BEEN MOVED, PREVENTING PROPER VENTILATION OF THE SUMP SYS. DRAIN LINE & VENTURI CORRECTED, & SUMP CAN & ASSOCIATED LINES CLEARED OF ACCUMULATED FUEL & OIL MIXTURE. MULTIPLE GROUND RUNS & OPS CHECK FLIGHT CONDUCTED. REPORTED HUMMING SOUND & UNUSUAL ODOR COULD NOT BE DUPLICATED. RETURNED ACFT TO SERVICE.