Are you really installing BRAND NEW power steering pumps?…..or remanufactured ones from China?
Honestly, I haven’t had to replace many PS pumps over the years.
The noise is most often due to air entrainment … or fluid drying out thus wearing smooth parts of the pump.
My 2012 Outback had the PS pump replaced due to TSB (Technical Service Bulletin)
It wasn’t loud… just not a lot of ‘power’ in the steering.
Have you considered using a temporary (external) tank? … I’m wondering if the tank itself is somehow allowing air into the pump.
Be aware—the tank usually has a fine mesh screen about 1/2 way down inside it. This screen filters the fluid and helps aerate the fluid. (air bubbles tend to stay ON the screen) Have you inspected your tank to verify that the screen is not clogged by the “incorrect” fluid you mentioned.
Some people have been known to remove the tank, spray the inside with carb cleaner and let it dry in the sun. This is often enough to clean the fine mesh screen.
