Car is an 82 Trans Am with an early TPI drivetrain from a Camaro, all stock.

Here’s the story. The compressor on the car was shot and replaced about a year and a half ago. The first compressor they put on made a grinding noise when the clutch engaged. They replaced it with another one. It did the same thing. They replaced that one with a third one. It does the same thing. All three worked fine, except for the noise.
The rep at the manufacturer said that the noise is normal, and is from the clutch having to break in or something. I thought it was BS, but didn’t want to put another compressor on.

So, a year and a half later, the compressor still makes the noise, the same as it always had.
Over the weekend I tried to diagnose it a bit. Going on a suggestion that maybe the clutch isn’t engaging all the way due to not enough volts, I tested the volts across the terminal and got around 9.5v. I noticed the little resistor that was going across the terminals and decided to try to clip it and see if that makes a difference. I clipped it and got 11.5v, but the noise is still the same. I also noticed that it didn’t matter, as far as I can tell, which way the terminal went on the compressor. I guess the polarity of the clutch magnet doesn’t matter?

Any insight into this grinding noise, whether the resistor is important, and if the polarity of the plug is important, would be appreciated.
Like I said, the thing works fine AFAIK, aside from the grinding noise.

Thanks