There is some noise in all power steering systems. The most common noise is a hissing sound when you turn the steering wheel and the vehicle is not moving. The noise is most evident when you turn the steering wheel while applying the brakes. There is no relationship between the noise and the steering system performance. Do not replace the valve unless the hissing noise is extremely objectionable. A replacement valve will also have a slight noise. A replacement valve is not always a solution for this condition.