Let me guess, you have a Fluidyne radiator or another of similar thickness? I had what I thought was exactly the same problem.
Do this simple check: does the PS steering make more sound when you're turning left instead of right, or vice versa? Does it only make sound when your fan is running? If so, it has nothing to do with your PS -- your fan blades are hitting the bottom of your airbox, but only just barely and only when the frame twists ever so slightly.
Assuming this is your problem, you have two basic solutions I'm aware of: 1) modify airbox to avoid hitting fan; (2) swap fans for the Valaya Racing fan kit. We actually installed this kit this very evening, and it kicks a** -- watched the twin fans bring my coolant temp from 215 to 195 in 25 seconds with the car idling. I'll post pictures shortly, but in the meantime you can call Valaya (408.448.8811) if you want details.
