There's no way this is a normal sound because it happens even when loaded in a cold and dark state. It happens as soon as I load the plane (even in the 'free flight' window that opens when you first open FSX) and it is at least twice as loud as any other sound the plan makes while I'm flying it. It sounds like other people are experiencing it, though, so at least it's not something I screwed up when I installed it...always a relief.