What was found
DURING CLIMB AT AROUND 10000 FT, THERE WAS A LOUD POPPING NOISE FOLLOWED BY LOUD NOISE OF AIR RUSHING UNDER CABIN FLOOR AND DIFFICULTY MAINTAINING CABIN PRESSURIZATION FOLLOWED BY NR 2 A/C PACK OVERLOAD MESSAGE, ACFT RETRURNED. MAINTENANCE INSPECTED AND FOUND COUPLING ON COOLING PACK CAME OFF, ADJUSTED COUPLING AND SECURED, OPS CHECKED GOOD.