Ya when the car is running you can't put the stethoscope on the bolt for the alternator pulley because it too is spinning, so all you get is the sound of the stethoscope rubbing the bolt. I stead I put it on the alternator casing as close to the pulley as possible and I couldn't hear the exact noise, but when spinning it by hand with the belt off, you can hear a bit of a clicking sound which might be it (since the other pulleys don't make such a noise.
The weirdest thing is that the only place I can really hear the noise with the stethoscope is where my map sensor is. It is an LSJ map sensor and it is held firmly in place with a piece of metal and the screw on the manifold. It has zero play, but when I put the stethoscope on the metal piece I can hear the whining noise more than anywhere else. Its not coming from there though, so it must be sound reverberating in that area (since its most certainly pulley related given what I've mentioned so far).
I'll try an alternator and see where that takes me...
2008 Cobalt LT // 2.2L Supercharged w/3.1 GM stage 2 pulley