I am getting a horrible whinning sound at times from my car. It sounds like the power steering pump. I can hear it very clearly inside the car (Like its coming from the steering wheel), but when i pop the bonnett and try source it I can't hear it. As the revs go up it seems to dissapear and I mostly have it when the car is cold. I cannot seem to find the power steering pump or even the resevoir for it! The car is a 1.8t vRS. Can somebody please help!

The reservoir is on the left hand side of the engine bay between the coolant expansion tank and the washer fluid reservoir and has a dark green cap