Audi A6 wagon- power steering - funny noises

I have an Audi A6 Avant wagon. There is a squeaky kind of noise coming from the driver side front. It doesn't start making the noise until the car is warmed up and gets progressively worse and more constant as I drive longer distances. It happens when the left front wheel goes over even the slightest bumps in the road. The sound also happens when i turn the steering wheel to the left and back to center but not when i turn it from right back to center. I have check the level of the hydraulic fluid and it was low. However the sound started again even after the fluid was filled back to it proper range. It could be a bad rack and pinion, but i am not familiar w/audiCar Repair Talk's forum.