I've read before that the Atwoods are quieter, but I have never been able to quantify the sound difference. If anyone has a decibel meter and one of these Atwood heaters, I'd be interested in knowing the decibels at, say, 3 feet away. Or if anyone can find db ratings in the specs, let me know.
Incidentally, in searching for this info I came across a pdf of the installation instructions (with some specs) for the 7900 ii and 8000 ii series Atwoods. The sheet begins with this statement: This furnace design has been certified by the American Gas Association and Canadian Gas Association for installation in recreational vehicles...