Thanks for the info. FWIW I’m only interested because I went through a battery recall on my Bolt EV. Very similar situation actually, like the water heater the affected cars was small, a few percent at best (same here according to the report), and fault too was with a supplier - LG in this case. They didn’t do quality control on the cell tab alignment. A couple cars caught on fire and rather than have a PR disaster GM took it on themselves to replace all the batteries. And there too there was a parts supply issue, not surprising when suddenly there’s an order for thousands of new batteries (or water heaters). GM took a write off of a few billion for that one.
The best measurement of quiet is your ears in a side by side test. The RMS noise meters (I have one) are useless for this as they just measure overall averaged dB, not things like spikes or variation (very annoying) or frequency content (high frequencies are much more annoying compared to low). The ear knows what bothers it.
Listening to my Truma now, the fan is just fine, wouldn’t mind a little slower blower to drop a few dB but it sounds like white noise you’d use to go to sleep to. The main thing is the roof compressor has a mid band edge to it (sounds like “urhhhhhhhh”, its around a G below middle C so not high around 200 Hz maybe). Not loud or super annoying but that’s the worst part, if that could be reduced it would be hard to argue with.