Tighten the four mounting bolts from inside. You will find them loose.
I have replaced both of my A/Cs. After a month you need to tighten them again. The foam seal collapses.
Full Time 2000 Dynasty Regent FD, 8.3, Banks Turbo, 5" Diameter Exhaust, 475 HP 1425 Torque, FASS system, towing 05 Pilot 1500 Watts solar 800ah lithium & E-Bike