Supercharger, Power Steering or ...

So I have been driving my 90 SC that is the middle of a restore to work about 2 days a week (100 mile round trip) and the car has been running flawlessly until yesterday when upon exiting the highway I hear somewhat low pitch growl/whine combo that instantly reminded me of a power steering pump/belt problem.

That would have been my diagnosis if not for some other symptoms:

1. This growl/whine (for lack of a better word) increases when throttling in park even when the steering is not touched.

2. It is not as pronounced at higher RMPs while driving (say on the highway)

I am a neophyte mechanic (but learning) but I have heard this sound before in many cars, so I am doubting its the supercharger (which was rebuilt 3 months ago).

So am I on target for power steering? Could it also be a belt (even not PS related)?

What are the symptoms of a bad harmonic balancer?

What is the best way to dianose, Supercharger, belts and power steering to find my problem?

Thanks guys!

You can remove the supercharger belt to see if it is the cause. Car will run just fine without it.

Well, to rule out the SC, just take the belt off the SC pulley and start it up. If the noise is gone, then you know it was the SC. If not, then shut it down, put the SC belt back on, and take the main belt off. If the car starts and still makes the noise, then it's not in the belt or accessories. If the car starts without the noise, then it could be the PS pump, alternator, AC compressor, or jackshaft bearing. If the car doesn't start at all ... well, then you probably have a bad balancer and removing the load from the crank pulley allowed the harmonic balancer and the crank sensor trigger wheel to shift around. And if the crank pulley is noticeably wobbling ... then the HB is bad (unless the pulley bolts are loose). One other thing you can do is, while the car is running, take a long section of plastic tubing and put one end to your ear and move the other end around near the accessories. The noise will be much louder when you point it at the problem component.

Do keep your fingers away from the moving belts! (The slowly disappearing bruise on my finger asked me to tell you that...)