I've owned 6 coaches...2 of them being class A diesels (vectra & journey) both bought new. All of the coaches had not only wind noise but the noise of the cabinets, some squeaking and creaking. Not terrible mind you but enough to question it.
I've driven 2 coaches that made absolutely no noise, none, no wind noise, no creeks and literally silent down the road. They where a foretravel and a prevost XLII. Even though my current coach is the quietest and it is a truck conversion, it still gets wind noise but no noise in the cab from the components. The only thing I can think of that is really different is that the foretravel and prevost have bladders that seal around the slides and doors once the coach is aired up. Maybe other high end coaches have this also but I have not driven them.
Sooooo, my conclusion is as the price goes up the noise goes down. Otherwise it is pretty normal to the industry.