I just flew my P4 for the second time. When I powered everything on I notice a very faint sound and not sure if it's normal. The only way to describe the sound is it sounds like a kid put a card in his bicycle wheel if anybody knows what I'm talking about. It's the only way I know how to explain the sound. Other than that it flies perfect the camera works perfectly and I don't see anything wrong with it so maybe this is normal?