Causes of high-frequency vibration through steering wheel?
 

Does anyone have any insight on a whirring variable vibration through the steering wheel that is quite noisy at slow speeds. Especially noticeable when turning hard left or right at a stop. The PS pump was replaced last year (according to prev. owner's records) but I am inclined to guess this is pump related as well.
Any thoughts appreciated.
Thanks in advance.
2002 A6 3.0 wagon with 131K

I had this problem after changing a power steering pump. I took the car to my local oil change place. They offer a flush for the Power Steering, it was like $38.00. It solved the problem. I think there was some air in the lines as well as some debris still in the system. Depending on where you go, the prices can vary from $30-$80 for the flush, shop around.