Yes it is quieter there and for another that diesel smell in the sleeper is very irritating on trains like the City of New Orleans where there is no baggage ahead of the sleepers any longer.
Actually that has more to do with the lack of a Trans/Dorm, than it does with the lack of a bag. It's the Trans/Dorm, with its head end door that connects to single level cars that keeps the exhaust out of the Superliner cars. With a single level consist, everything is below the stack level of the P42 so you don't have any problems. But with the Superliners in general, the "front door", if you will, is right at the stack level.
Without a Trans/Dorm's lower level "front door", you have a problem. I've been in a Superliner with a bag between me and the engine, and no Trans/Dorm, and the exhaust was still a problem.