Installation and maintenance of AC with no lower unit

I haven't been inside of those specific Class As with the AC running, but typically the full ducted systems (supply and return) are heavenly quiet.

I say typically, because the Mach 8 units on our winnebago are not as quiet as some - the low profile units, sitting on a fiberglass roof and sytrofoam insulation tend to make a lot of mechanical noise and vibration.