I only have experience with one model and I am no expert, but I have read the opposite about new machines. I have read opinions from long-time users that some of the larger, older machines were quieter than the new ones, because the bigger machines had more sound insulation. I have a ResMed S8 that recently had to be replaced due to a malfunction. The first machine was reasonably quiet. The mask actually made more noise than the machine. My wife said she was able to get used to the sound pretty quickly and she is very noise-adverse. The interesting thing is that the replacement machine, even though it is the same model, is noticably quieter than the first machine. So the first machine may have been defective all along, I don't know.
I can't imagine any machine is quiet enough not to take some getting used to, though. You'd be surprised what you can get used to. When I was in the Navy on an aircraft carrier, by bunk was just below the flight deck, right under a jet blast deflector. When planes were turning up, my roomate and I could shout out loud, but still not be able to hear each other. We slept through that routinely and no, I do not have any hearing loss.