knock noise

What is your question?

When the car is not moving and the steering wheel is turned there is a knock sound. I have had the suspension checked out and everything is tight. The only thing that the mechanics could think of was the driver side strut bearing (upper). Is this normal and if it is the bearing, is it crutual to get if fixed. Would the bearing be replaced or should the struts be replaced. The van only has 55K on it. thanks