Noise from the power steering unit

[hcander]

Power steering makes high pitched noise off and on, mostly on, at idle and sppeds up to 30 - 40 mph. Local shop replaced pump and indicated the new one would make a similar racket for a couple hundred (200) miles. It did so then stopped. After about 400 miles the noise has returned. Very annoying.

Any ideas out there? Any help appreciated.