WW2 movies with their dubbed-in sound effects for cinematic effect can't really be used as a guideline for how airplanes sound from inside the cockpit.

But like Rip says, how can Hollywood be wrong? LOL
I do feel that engine sounds changing with airspeed is one thing that is currently missing from the sim. Even from inside the cockpit of a real airplane, its fairly easy to judge airspeed from the overall noise that the airplane is producing. Wind noise can change dramatically with airspeed changes. Prop pitch is continuously variable as is the power that the engine is producing (depending on airspeed and pitch attitude) by the prop governer. The bigger the "bite" that a propeller takes, the greater the air is disturbed and with it noise produced. The greater the manifold pressure, the louder and deeper the engine sound gets. With a constant speed propeller, the only thing that doesn't change is the rotational speed of the prop for a given, pilot selectable, RPM setting. Everthing else is variable including the engine loudness, prop noise and wind noise.
MiG