A noisy rig will be real short built on an E450 chassis with a lot of extra load margin so you bounce the house down the road.
Our 23'-8" long rig
HERE is built on an E350 and no slide out. It has just enough margin to offer a smooth-ish ride. Even with that, to get the rig quiet, it took a few years to chase down the worst of the noise-makers. I have to say that I was quite successful with much determination to have a quiet rig. Our rig really does run fairly quiet.....that is until the V10 starts to torque it up.