Audi A6 Power Steering Noise

I have a 1999 A6 with about 85000 miles. Recently I have noticed a whinning noise when I turn the wheel sharply when going slow. No noise when going fast. The noise seems to be coming from the drivers side front of car. I checked the fluid level and it is fine. The unusual thing is that it only does it after the car has been driven for a while and is hot out. Could it be the belt, pump bearing, other steering linkage?

Thanks

It usually means that it is sucking air, cavitating or foaming fluid.