Our new 2006 Newmar Mtn Aire is amazing as far as quiet goes. The engine muffler system and the insulation in the engine compartment combine to reduce the noise levels significantly. I haven't measured the dBA levels but I would guess they are below the 80 level in the bedroom. In the cockpit, you can't hear a thing. I have to look at the tach to see if it's running. Our old 2002 Islander, although a good coach for us, was very loud in that regard. The engine noise was not muffled or insulated well to reduce the noise levels to really comfortable levels.
The Newmar is amazing. I hope it maintains its current silence. With good inspections and care it should keep its noise reduction characteristics.
Good luck with your Newmar!!!