This has been going on for a lil while now and I've taken the car to 3 different Nissan dealerships and they all claim to not hear or notice the problem. It did seem to happen after I had my Greddy Evo2 Catback exhaust installed but whether or not it's relation I'm not sure.
You can't hear it as well from the passenger side, much easier to notice from drivers. It sounds like hollow/metal type rubbing or rattling sound when accelerating. It ONLY happens when accelerating and usually near the 3-3.5K RPM mark and 6k+ mark. It will NOT do it when in Neutral or Park revving, only in gear.
I have a video here that you can listen to it, easier to hear when I put the camera on the dash near the vents. I can feel tiny vibrations in the gas pedal when it happens and it seems to take a bad performance hit too. It seems like the radiator fans come on more then they should too but I might be paranoid now.
Another thing, it never does it when you first start the car.. But after it warms up the problem starts and the performance seems to degrade... Any ideas I'm stumped...'
YouTube - 350z Rubbing Vibration Noise when Accelerating
Mods: JWT Popcharger, Greddy Evo 2 Catback Exhaust, Berk Aluminum Z Tube, Kinetix V+4 Upper Plenum
Btw- if you don't have good loud speakers, it's much easier to hear the noise if you have some good headphones.. Thanks for the help.