The only time you put stuff on the belt is when you have V-belt and you put it on the side that doesnt touch the pullies. On serpentine belts you DONT put anything on the belts. I know PS is always loud. They make noises brand new and old so you cant get rid of that. If your PS fluid is low they are louder. Try some lucas power steering stop leak. That made mine quieter
If you are talking about belt squealing, you can try some belt prep that softens the rubber and makes it a little sticky. Also, try buying a new belt. Or a belt that is 0.5 inches shorter than the current belt. There is also a product called instaboost made for supercharger belts that makes them really sticky and keeps them from squealing.