^^^
I owned 2 other Nissans before. I've had rattles successfully repaired on my former Maxima. On one case, there turned out to be some loose wiring/cable under the HVAC panel or behind the coin holder (sort of where an ash tray would be, if the container weren't felt lined).
On my Z, I had a buzzing (from vibration) rear view mirror replaced but eventually it also buzzed, after the warranty ran out. If I had any rattles in my Z under warranty, they were fixed too... My memory's foggy.
On my Z, I had a external weird squeak when the car was cold. Service writer reproed it by driving my car forward and back a few times and proclaimed it was the axle click. I'd been reading about the infamous axle click TSB but never knew that was the sound. The repair worked!
Sounds like you should try another dealer.