As far as I know, we haven't had anyone else complain about the sounds sounding like an "old windmill". Here's a video showing the exterior with engines running that sound like a, well, a DC-3.
The sounds were recorded in stereo, from a real DC-3 by Vance Dylan at Sonic Solutions. No, there is nothing you can do to change them and we have no plans on doing anything further with them. Hope that answers your question.