That noise is normal. Both of my 350's did it and both of my 370's have done it. It is not the throw-out bearing as it was though when the issues first started. That noise is a characteristic of the Z. Everything is ok.
I have less than 3,500 miles on my Z and is doing it. I think I will be worried the day the noise is no longer there.
For reference and peace of mind read the following:
370z clutch noise?
and this one:
Transmission / Clutch - Rattle
and this other one:
Depressed Clutch Noise/Vibration