It sounds like you need to remove the grill from your a/c and check the hold down screws in each corner. They are used to hold the a/c in place on the gasket. This gasket is originally approx 1" thick but compresses over time and the screws get loose. Just tighten this up a bit, but be careful. They only need to be just a hair past finger tight.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof