Rob76

Hi. Just got back in to BMW's after buying a E70 3.0D M Sport with 7 seat option as our family bus. Its only 2nd week and still loving the change. I have noticed though that on some occasions there is a noise comes from the engine bay once engine has been turned off. It sounds like mechanical whirr...like a small pump or fan then its followed by the sound of a pressure release ( gas or air )? Anyone able to tell me what this is? Cheers Rob