A few tips before you go and replace it:

1. Check to make sure the belt is tight. If you press on the belt it should give a little but not anything significant. Check the tension compared to the other belts.
2. "Bleed" the steering by turning it from full lock on one side to the other, about 5 times slowly. This allows air to make its way out of the lines.
3A. After bleeding the system, open up the reservoir and check the fluid level on the cap. Refill as needed.
3B. If the fluid was low, check the boots on the inner tie rods for leaking fluid. After a long wheeling trip it's possible they sprung a leak.
4. If the system is still making noise, clean out the filter.
5. O'Reilly's sells synthetic Asian vehicle power steering fluid. Not everyone will agree with using it but it quieted up my power steering pump completely for $10. Extremely satisfied with the product.
6. If you still have the noise, replace the pump.