Hi. I have just noticed that my Z4 coupe is making a whining noise, like a bi-plane taking off, when I put my foot down to accelerate rapidly. When I leave off the accelerator the noise slows like a bi-plane coming in to land. At first I thought turbo noise but then I thought this is a naturally aspirated engine so it has no turbo. I do not think it was doing it before but then usually have my music on so might have missed it. Is this normal or should I be getting it checked out. Any ideas what this could be?