Just picked up this Hr Z 45k miles. Apparently it had a stage 2 clutch change and maybe flywheel change?
here are the issues I can't stand..
1. When clutch is let out a faint water running noise is present.
2. When I'm in gear ( on light/regular acceleration)I can hear this high pitch chattering/rattling noise outside the car that goes all the way to like 4k rpms? (Goes away when pressing down on clutch)
3. It goes away more when I'm at higher speeds or I straight WOT.
4. Also the bite point is extremely high compared to my last car (g35 2004).

I heard this can be because of a lightweight flywheel or clutch? Any help I can hear it over my exhaust it's so annoying.

 

Sounds like you found the reasons the guy sold it, sadly. It really is hard to say without knowing what was done and by who, but in my experience a lightweight flywheel or clutch will simply give a bit of mild chatter or vibration, what you’re describing sound like and install issue, or a part issue.

 

The "running water" or commonly called "cement mixer" noise is a result of the lightweight flywheel. Pretty normal. If it drives you insane, you can either go back to stock, or try a heavier single mass flywheel. I know a few vendors sell some mid-weight options.

 

A lightened flywheel will cause the gearbox chatter you're hearing. You can look into this phenomenon by searching torsional vibration. The other noise you're hearing at idle/neutral is usually the clutch throw-out bearing or transmission input shaft bearing (or both). A high pedal engagement point isn't terribly uncommon on these vehicles, even on the OEM FW and clutch, but this is typically a good indicator that your clutch material is wearing out.

It sounds like you picked up a clean Nismo if it only has 45k miles. I would just bite the bullet and replace the clutch, flywheel, and CSC all at the same time. Go with a heavier/reputable Single-Mass FW and a quality clutch. There's honestly no need to get a Stage 2 clutch on an NA Z. Once that's done, you should have a nice daily driver.
Good Luck!
-Icer

 

I have never heard that noise described that way but it is the perfect desription