And, are you CERTAIN it's coming from the rear, and not the transmission?
If the shaft gearbox is out of oil, you've likely found your culprit. If not, a friend with a moto-lift that can get the back tire off the ground and a quick run through the gears whilst probing with a mechanic's stethoscope will pinpoint the noise.
I don't need to tell you to keep all fingers out of any moving parts, or to make absolutely certain the bike is securely lashed to the lift while operating, do I?
I knew you knew that.
