This has been occurring intermittently for about the last 7-8 months:
When making low speed turns, i.e. in a parking lot, I'll get a sort of high frequency "shuddering" feeling in the steering wheel, and the engine will be noticeably pulled down, and it's accompanied by noise from the power steering pump. It's as if the system is somehow overloaded, though it occurs with the car moving and stationary.
Again, since it's intermittent it's been very hard to track it down. It does it warm or cold, too. Fluid appears to be clean and the level is right.
The pump noise will also come and go without the shuddering. I almost replaced it about 6 months ago then the noise stopped, so I took the pump back to the parts store.
I do know the steering rack was replaced when the previous owner had the car. It now has approx. 137,000 miles on it.
Could it simply be the power steering filter in need of a change?