What was found
SMF - AIR TURNBACK - FLT 544 - AFTER TAKEOFF, DURING CLIMB EN ROUTE TO PHX FROM SMF, CREW HEARD LOUD NOISE FROM THE NR 1 ENGINE AND NOTICED NR 2 ENGINE OIL QUANTITY GAUGE DROP BELOW ONE. AIRCRAFT RETURNED TO SMF AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE INSPECTED AND SERVICED THE NR 2 ENGINE IAW BOEING 737-300 AMM 71-00-44-01. NO DEFECTS WERE NOTED AT THE TIME. ALSO RAN ENGINES AND PREFORMED AMERICA WEST AIRLINES TASK CARD F2A77001, AVM INTERROGATION, ON THE NR 1 ENGINE, WHICH ENGINE WAS WITHIN OPERATING RANGE. AIRCRAFT RETURNED TO SERVICE.