A common issue especially with the 2009-10 USDM GT-R is the dreaded Bell-Housing rattle.
This appears to be a design problem in the bellhousing machining process. The clearances are incorrect, which can lead to some massive float in the shaft, which is where the horrible noise originates from.
Nissan has released a revised bellhousing, part number: 32040-kb50a. There are also aftermarket companies that manufacture shims to correct this issue.
Inside of bellhousing, input shaft:
Output of housing:
These shims go at each end of the shaft and stop it from moving back and forth, locating it in the correct manner.