How do you change a power steering hose in a 1989 Legacy wagon Is the symptom for low power steering fluid a whining noise?

Yes, if power steering fluid is low, you will get a growl/whine noise from the pump. Make sure where the leak is before replacing parts. Add more power steering fluid (and pleez do not use the stuff with leak-stop in it), try to mop up whatever oil is around the pump, lines, and rack, then drive the car a bit. Let car cool off a bit, then look carefully for where the fluid is coming out. Most Subarus go to their deaths with all original steering components in place, regardless of mileage or age. If they fail, the steering rack is the first thing to spring a leak, then the pump seal, then the hoses (in decreasing order of failure). It is best to use special power steering fluid-- auto trans fluid can be used but is not as slippery, and the pump wears a bit more. That being said, your pump should function for 50 to 100,000 miles with just auto trans fluid in it. Service access to the steering rack and lines is not the best-- make sure you are capable and have the wrenches before tackling a hose replace.