I initially thought it was coming from the transmission area because of the way I heard it so well in the cabin and even through the handbrake vibrations. In my case, though, it was the alternator. I changed it today, and the sound is gone. I would highly recommend the HF stethoscope to help you narrow down the location. The indie mechanic was really leaning toward it being the flywheel until they removed the belt, and the sound stopped. Good luck!