Turboprop Simulations figured the beaver in FSX doesn’t sound the way it should, and released a soundpack for it. They say about their product “…. Enjoy the full realism of engine sounds from the DeHavilland DHC-2 Beaver the way it was meant to sound. Bush pilots and simulator fans will enjoy the loud piston engine quality from the interior and outside of the beaver. All audio was kept at full quality from their original recordings taken resulting in a real experience you have to hear to believe!…”. Available here on simMarket.