There are 2 lines, pressure line from pump to rack and return line (much lower pressure, sometimes uses rubber hose for part of it) back to pump.
The pressure line is usually shorter and less expensive. The return line can be very long because of a “cooler” section that is located behind radiator, so it runs from behind engine to the front of vehicle, across the front, and back down the other side to the pump.
Access (for line replacement, depending on which line) is very difficult on some cars and is labor intensive.
Do you know which line is leaking and did you get an estimate?
I have found good quality aftermarket return lines, but it’s the labor that is usually quite expensive.
A return line (the low pressure one) can sometimes be repaired with rubber hose design for PS use.
I had a leak in a return line near the radiator in the “cooler” section of the line (caused by a stupid metal clip on a wiring harness that rubbed a tiny hole in it). Repair cost estimate was very expensive, so I used a mini-tubing cutter, cut out a 1/2" length of the tubing and repaired it using a 3/16" brass compression union ($3) from the hardware store. Total repair = 3 bucks!
Low fluid OR air entering the line (like through a leak) can both cause a whine. Trust me, I know.
I was getting that until I repaired the leaky line. The noise stopped as soon as the leak did. As long as the pump isn’t damaged that should be the result.
I gave our old Impala to my son to use about 5 years ago. It had a leaky PS pump that would sling fluid up where you could see it on the hood. Before I could do anything with it, my son bought and added some “miracle in a bottle” PS leak stop.
I would have never done it, but I didn’t say much (bit my tongue) because the damage was done I thought.
I’ll be danged, but that stuff stopped the leak and it’s been four years and another 100,000 miles!
Since then the car was used by my daughter for a couple years and then we got it back.
The PS is still going strong with the “miracle in a can” and the compression union splice is just fine. Car has over 300,000 miles and is 17 years old.
Hope that helps. Keep talking.
CSA
EDIT P.S. I believe there is also another short line on the rack that runs from one part of the rack to another part. I’m going to have to look a diagram.