Hopefully someone can help me or has had this issue before.

68 roadrunner. I converted it to PS a few months ago. Box is from my 74 challenger, was a sound box before i swapped to manual .

I had a Trw pump i threw on, it worked, no noises. But it leaked like crazy and also felt WAY over assisted. I had some saginaws laying around.

Converted it to a Saginaw. Not sure off what, could of been mopar or GM but they all look similar and bolt up. Every thing was fine for a few days . Until today I saw the belt was a little loose so i snugged it up. Geez , After i did that the pump started whining and gets louder as rpm climbs. Thought bad pump ( it was used) put on another used , same thing. Put a 3rd pump on . Same deal! Im using normal PS fluid, belts snug.

What should I check next? Could the pressure line be collapsed internally like a brake hose? No bubbles in the fluid when running. Any suggestions would be appreciated! Thanks!

Did you bleed the pump by going from lock to lock slowly a couple of times?

Yes. Even took it for a few mile ride. Whines when reving up in neutral etc. sounds like I have a gear drive when I'm driving.

Any chance there is a kink or restriction in the return line? That could make it whine.

Low PUMP fluid is a classic cause of that & something might be resttricting fluid flow. As said I'd pull/check the HOSES. all that is left is the ST BOX itself (restricting flow somehow internally)