Thanks for everyones input. This saga keeps getting better. I agree with Woody that the SC is NOT engaged when the sound is heard. Activating the AC does NOT activate the SC clutch as I had previously suspected. I have now ~$1250 into a second SC and it came with a new Code-3 bearing just like the one I had installed a few weeks ago to try and correct the problem. So now with a 2nd SC and 2nd pulley the noise is just the same as before. No better no worse. I can shoot another video and it would sound the same. Pulley gap is set to .3mm and both old and new unit had the same single shim. Turning on the AC really makes the noise as you hear it on the video. Turn it off and the sound almost goes away (but not entirely). No noise is coming from down low where the AC resides. It's up top. Idler is new and other accesories seemed ok when I had the belt off during the SC swap. Both dealers wanted me the spend big bucks on a new SC and MB tech said the clutch is part of the SC and it can not be repaired at by the dealer. I need to talk to the folks that rebuild these and get their input. New SC runs great but my old SC ran great as well. I have a lot of video footage on the job I just completed (more YouTubes to come). How many of you know where the real intercooler (the one that sits under the SC) is made? Hint: Taco-Bell.

I'm not sure what to think. Noise comes from top side, not bottom side. Can not imagine that two SC's would be bad, making the exact same noise. MB tech said he had not ever heard of an AMG SC going bad. I'm missing something for sure. Had it all apart and both SC's and pullies looked and felt very very OK. No vibration. Rotor inspection showed no signs of wear or tear. Car performs very well except for the noise.

To date: (Car has 42K miles)
New (used 18K mile) SC - $1000
New Code-3 Pulley bearing - $35
New idler pulley - $50
New injector o-rings - $30
New intake gaskets - $20
Labor/diag - $100
Noise - Priceless