These sounds were custom recorded from a real DC-3, inside and out. In my opinion, I believe they've done a great job.
Also, it passes the "sounds different when you open the window" test, so that means the "experts" on the official forum will approve.
Do you really have to be an "expert" to know that sounds get louder when you open windows though?
Don't worry about the startup Jan. The entire suite was recorded on a real aeroplane from the moment the hydraulic hand pump goes up on its first stroke to engine shutdown. It's as real as it gets.
I had my first flight as a 12 year old on a Cambrian Airways DC-3. It's something I will never forget.
Dang! So apparently it is not impossible, after all, to build a really spot on awesome sound set for planes in this sim! Can't wait for the release!