I have heard people complaining about the whine from the p/s pumps for years and wondering if its because they put in the wrong fluid,I had the cooler develop a leak in my 95 so I got the owners manual out and it says type F and now that its fixed it barely makes a noise. I always used ATF in my 70s and older Fords and will have to admit when I bought the 87 I figured it used the generic p/s fluid like the rest and that pump made noise and I never bothered to read the manual.

 

There's a number of possibilities that could cause the whine. Yes, transmission fluid, type F, or whatever type is recommended for your model year truck. Also, I have read that aftermarket power steering lines may cause a whine too. I had a line blow on my 02 and replaced it with a generic line, and it started to whine. I attributed it to running the pump low and thus causing some wear in the pump. I wasn't going to change the pump until it went out. I used synthetic transmission fluid, and it never got better. last year, I did some major work in the engine bay. I opted to change the power steering lines with Ford/Motorcraft lines, and the whine disappeared! Like I said, I believe there's a number of possibilities.