how To Silence a Loud PTAC AC Unit?
It is possible the coils are full of dirt on the outside coil. They can be hosed down. Don’t use high pressure water that will fold the fins over and make it worse. Also when flushing make sure the water is coming out the drain. I put several gallons of water on my sister-in-law's floor cleaning her window type unit, but it worked better after that (or she was so hot from mopping just the fan felt cool). Also verify the inside filter is clean and dust free.