Hi, I just got my Black G35 coupe 6MT last week and I noticed something pretty strange when I put the car in neutral. I had the car parked, and turned on, in my driveway in neutral. For some reason I was pushing the clutch in and out. To my surprise, I heard a faint noise and the RPM's actually budged when I released the clutch all the way. Isn't this strange?? The car was in neutral, why would it do this?

 

Well, belive it or not, pushing the clutch in and out is actually doing something. And that requires power.

I would bet the master and slave clylinders required a bit more power (from you using the pedal on and off), and the engine complied

 

Even though you're not in a gear, the input shaft is still attached to the motor when the clutch is engaged. When you disengage the clutch, you are also disengaging the input shaft and a few gears from the crank, which (temporarily, at least), raises the RPM and results in a slight noise. See:

http://auto.howstuffworks.com/clutch.htm
http://auto.howstuffworks.com/transmission.htm