What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO LAX. AT FL250 GREEN HYDRAULIC SYSTEM RESERVOIR OVERHEAT ECAM MESSAGE FOLLOWED BY A GREEN HYDRAULIC ENGINE #1 PUMP LOW PRESSURE ECAM MESSAGE. FLIGHT CREW FOLLOWED ECAM PROCEDURE FOR GEAR EXTENSION AND RECOVERED THE GREEN HYDRAULIC SYSTEM FOR LANDING. THE AIRCRAFT LANDED SAFELY AT LAX. MAINTENANCE ACCOMPLISHED TSM 29-11-00 AND FOUND THE POWER TRANSFER UNT (PTU) WAS OVERHEATING AND KNOCKING. MAINTENANCE REPLACED THE POWER TRANSFER UNIT (PTU) PER AMM 29-23-41 AND ACCOMPLISHED A SATISFACTORY LEAK / OPERATIONAL CHECK.