What was found
AFTER LEVELING OFF AT FL 330, CREW NOTED NR 1 ENGINE OIL PRESSURE FLUCTUATING SLIGHTLY AS THRUST REDUCED. IN ADDITION, AVM INDICATION SPIKED UP 2 UNITS, THEN RETURNED TO LESS THAN 1 UNIT. A FEW MINUTES LATER, A LOUD BOOM WAS HEARD FOLLOWED BY NR 1 ENGINE SPOOLING DOWN. CREW DECLARED AN EMERGENCY, AND MADE AN UNEVENTFUL LANDING AT BNA. INSPECTED AND FOUND METAL PIECES INSIDE FAN COWL. FURTHER INSPECTION FOUND A HOLE IN ENGINE ACCESSORY GEARBOX JUST AFT OF STARTER PAD. ENGINE CHANGE IN PROGRESS.