So it was more than likely the flexplate then? If it was you saved yourself a lot of $$$.

 

My car is undeniably the substrate as I can make the sound go away when applying light pressure with a pry bar wedged between the head shield and downstream cat. After I took the heat shields off the noise is practically gone. Being that the cats are so close to the transmission/engine block I was deff. worried at first that it was something catastrophic, but that's not the case. Anything off idle and the noise is long gone.

 

I'm going to say yes, partially for peace of mind and just due to the fact that it always seemed to get worse after highway driving and or spirited driving. You could feel the rattle in the shift **** while driving. The sound was definitely coming from the bell housing.

 

I never did try using a pry bar on the heat shield but I did hit the heat shield pretty hard to see if I could replicate the sound. I could feel a rattle in the shift **** while driving down the highway. There are quite a few others that have had issues with the flex plates in these cars and the 370z's. It seems to be the weakest link unfortunately.