As far as location of two units on the 2552 I believe one is along the centerline and between the microwave and pantry, the other along the centerline between both beds close to the bathroom door. Not a huge distance apart, but the two different 'rooms' they serve would provide some noise baffling between the two.
I've tried researching noise levels of different models from different companies and found precious little regarding technical specs or advertised sound levels (actual decibels) Different designs of different brands at different times can have significant impact on noise. Noise can emanate from motors, fan blades, etc. On the Coleman Mach 8 15,000 BTU unit, which I have, there were changes made to the fan blades over the recent years which reduced noise. On other companies units, the diffusers were recently redesigned to reduce noise. Personally, I think the diffuser makes a huge impact on noise. Trying to disperse and divert air by pushing it over fins and flaps creates a racket (remove your ceiling diffuser and see the difference)
Knowing as much (or as little) as I do now, I would have specified two non-heatpump units (one 13.5k and one 15k btu) with high CFM rates (they apparently range from 275-350 or so), multiple fan speeds and well engineered diffuser/motor/blade designs. For us, very low roof profiles (like our Mach 8) or savings of a couple hundred dollars (Dometic) are not as important as good performance and reduced noise. We like nice sunny weather but aren't terribly comfortable at temps over 100 degrees or at very high humidity levels, so two units would have made us much happier.
- Mike
