The gas engine in most RV's is the same gas engine that is in pickup trucks made by the same manufacturer. Obviously, if you have ever ridden in any of the newer pick-up trucks, gas or diesel powered, you know that the noise from the engine can be controlled to a level that is almost unheard in the cockpit. Some RV manufacturers do a better job with sound insulation than others. The facts are the insulation itself is inexpensive and it is something that most do it yourself owners could add later if they feel that the noise is objectionable.
I've got a big hemi gas engine right in the front of my automobile and you can hardly hear the engine at all. It certainly does not interfere with conversation.
By the same token, I've had a couple of DP's where I chased the whistling wind noise caused by window air leaks, mirror noise, and a front door that didn't seal as tight as when it was new.