Originally Posted by FR Steve L
but I'm getting a terrible whining noise from the steering column both when turning and even while sitting stationary
It may not be the PS unit.
Look at the main belt very closely for abnormal wear. Or you could have a pulley misalignment or perhaps a faulty belt tenstioner. With the engine running, AC and heating off, with the hood up, look and listen carefully and try to determine exactly where the sound is coming from while someone else gently turns the wheel. You might also want to crawl under the front of the chassis and look up under the engine to see there's any rubbing going on, leaking fluids etc, etc.