So I took my Z to Baker Nissan here in Houston yesterday. They drove the car around for a couple hours trying to find out where the sound was coming from. They said it was definitely not the TSB rear-axle issue (which they said they would have taken care of for free).
So they still have my car and are going to try to swap the drive shafts/rear end from another 09 on the rack for an engine replacement to see if it helps. If so, they will order the parts and install under warranty.
The worst that's coming out of this is having to pay for a rental daily, but oh well. I'll keep everyone updated..
Link to Youtube video of sound. For some reason embedding isn't working for me
YouTube - ‪370z Metallic Click Sound‬‏