2) With the A/C off. Clutches that have made noise on me were when they were free wheeling.
With A/C on, the clutch is locked together, so if you get a noise from the unit, it's most likely a bad bearing in the compressor. But that would be a different sound from a bad clutch noise.
Also a bad alternator bearing can make a grinding sound.
If you ever get a chance to catch it making noise at home, take off the serp. belt, start the engine back up, and listen for the noise.
Don't run it real long though since the water pump won't be flowing. And while the belt is off, you can spin all the accessories by hand, listen for any noise, or feel for any resistance or bad bearings.

 

I might have to do that. Especially since the noise is so hell-bent on not letting me hear it while I'm outside of the car. :P

 

Well, I've figured out what the problem is, and I'm glad to say it's nothing serious. And the one lesson I've learned from this long process is: rev the **** out of it, and the noise will present itself. :P

It's a broken baffle in my muffler, which explains why it sounded like it was coming from everywhere except the engine. It traveled along the exhaust, and was essentially being heard from every point along the car.

My favorite part is that you can see the muffler flexing as I rev, where the baffle is broken/flopping around. haha

 

i tried to point you in that direction.