Well, I'm at a real loss here. The whine was eliminated by going to 1/2" on the feed, return, and PBY lines as noted earlier.
The 3-point works perfectly and the power shift is fine. The system is quiet and smooth when you dead head the pump to check pressure at the valve. All is well as long as fluid isn't flowing thru the work ports via applying the control lever.
I've checked the strainer again. No debris. Changed the filter again, no change.
I looped the work ports to take the cylinders/load out of the equation. When the control valve is actuated you can see and feel the line with flow jumping and vibrating. You can also feel light hammering in the hard pressure line from the pump to the divider block. It really feels like air in the system but I have no idea how that could be and the fluid doesn't show signs of air bubbles. It almost feels like pressure chattering over a relief valve but when I dead head to a pressure gauge it's shows steady at 2000 psi.
I've done a fair share of hydraulic valve installs but this one has me baffled.