Got my Z back from the dealer yesterday. They replaced the whole regulator. The rattle is GONE
!!! The tech told me that there is not an individual part to replace, they just replace the whole regulator.
He did not know if Nissan had made a design change, so there is a possibility that whatever part came loose on my original part might get loose / start to rattle on the new one.
If you ever attempt to repair it yourself, it would be great if you could post a few pictures of the offending part and what you did to fix it.
See attachment for Nissan Door Regulator document. Maybe this will help.
Good luck.