I've got a '95 with a PS leak and got the whine when I started the car for the season. It has since gone away but I suspect it comes from air in the lines due to the leak. 3-rib versus 4-rib has nothing to do with it. That just provides a means for providing the necessary power to the PS pump. I don't have any experience but I find it damn near impossible to believe that having a little air in the system can affect the rack at all. I'm confident your rack is safe.
