Thanks to Doug Lewis. This is in reference to noise when the steering wheel is turned all the way right against the lock.

This problem is most noticable in the '91's. The problem is a pressure resonance in the high pressure side of the system. When the wheel is all the way to the right, there is a large amount of fluid in the right hand side of the rack and power piston. I believe this to be resonating like the water pipes in a house when you shut off the water too quickly.

The only way that I've gotten the noise to change is to remove the check valve and orifice in the pressure inlet of the rack. It is located just below the fitting for the high pressure line, inside the rack.

If you wanted to try this yourself, you can get to it through the driver's side front wheel well. Just remove the high pressure line from the rack and use a pick to remove the check valve (it should pull right out). Be sure that you have a new teflon seal for the fitting and reinstall the line. You'll need an 18mm double offset open end wrench to get at the fittings, but it isnt too hard. Refill the system and purge the air. This is done by turning the stering wheel lock to lock several times (10-15), holding the wheel against the lock with the engine off. This pumps the air out of the system and up to the reservoir. Refill again and start the engine and check for leaks.