Kayteg1 wrote:
Took the picture from our window via the screen, so excuse the quality.
The noisy furnace is on right hand side, when I see WH on left margin.
I think the exchanger overheat theory is right here, as I can hear the noise going for few minutes, shutting down and then a minute later coming again for a minute.

From your photo it is a standard rv furnace not a Aqua Hot for sure! Aqua hot will have a exhaust pipe like a car and is a common complaint as it runs to heat water in the summer when windows are open. and from the photo it appears to be a Gas Motor home ? (up-swept back is not typical of a Diesel pusher)but either way no high end hydronic heat.
Personally I would just walk over and mention noticing it cycling a lot and a strange noise (unlike your own furnace) and let them deal with it leaving it at that.By the way, If its cold enough to have the furnace on, your own windows should be closed,right? Even with single pane windows that should block most of the sound.That must be some noise if you can hear it that loud.