What was found
DURING PUSHBACK & ENG START, CREW RECEIVED A SEC 2 & SEC 3 FAULT. ECAM PROCEDURES CLEARED THESE FAULTS, THEN A LOUD GRINDING NOISE & BURNING SMELL FILLED CABIN. THEN THEY RECEIVED A HYD G RES OVHT ECAM MSG. FOLLOWED ECAM PROCEDURE & FAULT CLEARED SHORTLY. ACFT RETURNED TO THE GATE. TROUBLE SHOT TO A BAD PTU UNIT IAW TSM 29-23-00-810-812-A. R & R PTU UNIT IAW AMM 29-23-41-000-001-A & 29-23-41-400-001-A. LEAK CHECK & OPERATIONS CHECKED GOOD. PERFORMED GND RUN OF ENG & APU & PACKS. NO SMELL NOTED IN CABIN. CHECKED GOOD.