Good news: My dealer replaced the crappy Bose amp with a slightly less crappy Boss amp.

Bad news: Now my trunk rattles at 90mph+

 

change your crappy nissan dealer to slightly less crappy nissan dealer.

i had same issue and i noticed that my dealer didn't assemble rear bar right (they have to disassemble some interior pannels to reach the amp in the trunk) so it made annoying noise so i brought my car to dealer and annoyed them. they fixed it.
go to your z and open your trunk and make sure all the rear bar pannels are assembled right.

i hope this helps.