I thought it might be worth mentioning to everyone that I recently discovered that my superchargers sound different when they're cold as opposed to when they're warm.

While one of my superchargers was still in operation on my '92 and the engine was warm, I removed the belt and quickly rotated the pulley back and forth. I could feel a small amount of play, and the impellers made a clicking noise every time (or almost every time) I changed the rotation direction. So I concluded that the coupler must have worn out prematurely. I replaced that supercharger with one that I rebuilt the nose on (new bearings, oil seal, */c oil, and new OEM coupler). When the one with the rebuilt nose was cold, it made no such noise and had no play when I rotated its pulley back and forth in the same manner. After it had warmed up, however, it, too, had a little bit of play and made a clicking noise every time (or almost every time) I changed the rotation direction.

So please correct me if I'm wrong, but when diagnosing whether or not a supercharger coupler needs to be replaced, it appears that the pulley rotation test should only be performed while the supercharger is cool.

Recently I picked up another supercharger from a junkyard. Mileage unknown. Pulling the belt I rotated back and forth. There was no rotor noise to speak of, however the coupler play was horrible. Pulling it apart I used my hand to move the coupler first on the rotor gear and could see and hear the play, then on the snout with the same results.

As for the rotor noise on your old one, I would think that might be bearing wear that is allowing them when cold to slightly rub together. The tolerances are fairly close, they should not be making contact though.

I believe the pulley rotation test should only be used to CONFIRM what you already suspect is the source of the rattling noise at idle, not to diagnose the actual problem. If it'* not bad enough to hear at idle, it'* not worth changing the coupler.