could be alot of things the first thing that comes to mind is a worn belt,bad tensioner and or bad pump as you stated above its hard to tell without hearing or being able to locate sound myself...i would have an assistant turn wheel and you can use an auto stethoscope or what i use is a rubber hose about the diameter of your heater hose and approx 3 ft long. i hold one end of the rubber hose to my ear and scan under the hood for the source of the noise i would suspect if the noise is coming from the front of the power steering pump near belt the problem would be the belt or tensioner,and if the sound was coming from the center of pump or near or at pressure lines i would suspect a bad pump.....post results..