This is a question that should be easier to answer then it is. All manufacturers publish extremely confusing sound data, but they use different testing standards. With no industry standard testing procedure, each manufacturer has the flexability to test in the environment that suits their units best. It’s easy to get into a technical debate with no clear resolution, so here’s the best recommendation: Whichever brand you choose, make sure they use a 2 fan system. 2 fan systems are quieter than older 1 fan systems. The PTAC unit should have 1 fan that handles the condenser side and 1 fan that handles the evaporator side. The bottom line is if you placed 4 different brands side-by-side in the same exact room, it would be difficult to determine which unit was the quietest.