My coupler needs replaced and I was just doing some research and it seems like a lot of people have trouble distinguishing where it's the Idle Air Control Valve making the noise which is normal, or your supercharger couple is worn out and which is the culprit of the "rocks tumbling" sound. You can put your ear to the snout of the supercharger to verify where the sound is coming from. Here are two videos on you tube. The first one is the sound of a bad coupler. This sound is audible at an idle only. The second video is showing how to replace the coupler. I hope this helps somebody solve the problem.
Bad Coupler Noise:
YouTube - Supercharger noise
How To Replace The Coupler
YouTube - Replacing a worn out supercharger coupler on 3.8 GM engines
