Could be the power steering pump Could be the steering rack. My experience is that either usually leak when starting to fail. Power steering pulley could be failing. Could also be idle is too low.

Your symptom is typical of a bad power steering pump. I would troubleshoot further for verification.

What color is the fluid?
Do you get a squeal if you turn the wheel to either extreme?

__________________
X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas