What could it be?
I changed the pump and added fluid and I'm still getting a whining noise. on 1996 GMC 1500 Pickup
Which "pump" do you speak of? If your talking about the Power Steering pump, it may still have air in the lines. You can sometimes work the air out by simply turning the steering wheel from lock to lock about 8 or 10 times. Sometimes the air will work itself out after a few days of driving the vehicle.