Question on Borgenson power steering box

I’ve got the Borgeson box with my factory pump on the 273 in the barracuda. I added a small ps return line cooler. All I can saw is it works amazing. No troubles at idle or high speed. But my pump does become noisy (strange) at low speed parking lot maneuvering. Like pulling into a car show and being directed to a parking spot. I’ve taken it apart twice and all okay. It is a TRW I believe.
Syleng1