I can almost bet that's the throw out bearing

Sure hope so... I can confirm the Southbend clutch/flywheel combo is quite noisy at low speeds especially around 1,500 RPM. So this noise is definitely low RPM. I just have a habit of getting the car moving around 1-1.5k RPM (light throttle, of course).

Oil pressure is close to 30 PSI when I get it going in 1st. At idle, the lowest is around 20-25 PSI. There's almost 1,500 miles since the last oil change.

That's just clutch/FW noise man...

Even with the stock dual mass crap, I hear it from time to time.

Try and get a video of it if possible... The description is vague through the internet and it could be many things. Sounds a lot like some normal sounds, sounds like some not good things... Depends on if I'm being an optimist or a pessimist

See if you can download these files:
http://www.myg37.com/forums/2501490-post14.html

This is the "clacking" noise on startup on a G37, which I also get. It's the same sound. It's not a "ticking" noise either.

What's scary is the repetition and speed of the noise sounds like a rod. So far I've heard it a couple of times at low speed in 1st. Haven't heard it anywhere else, unless it's only the beginning. O_o

I'll try to get a recording whenever I have time.

I have a similar noise with light throttle between 2500 and 3000rpm on mine. It goes away in neutral or with the clutch in, so I'm doubting that it's motor related. It also started right after the turbo kit was installed with a new clutch and lighter flywheel.

The transmissions make all kinds of noises in these cars but they sound nothing like engine noises. The trans sounds are best describe as a cement mixer or grinder. It literally sounds like the transmission is full of rocks. That is normal when you load the trans at lower rpm or even at idle.

Engine sounds are very different. I can't process those zip files from my iPad here so ill try again later. If it makes a valvetrain type of sound on startup and only startup, I would first think maybe a timing chain tensioner was leaking pressure. If it does it all the time the engine is running at specific rpms and load, I would get a little more worried.

Make sure you don't have any of your DTCs disabled that would be related to cam sensors, cam timing, etc.. That way if its related to the VTC it might show a code. I've seen really noisy VTC gears in a DE before.

Does it do it more or less when cold or hot?

If we cannot Internet diagnose it, I would run it by a performance shop that is known for engine work and see if they will come out and listen to it. I would hate to make you paranoid over nothing... But it's just that if there is a serious issue, it's so much better to just stop before something actually lets go and takes out a bunch of expensive parts with it.

I'm convinced this is my issue, and it probably occurs at higher rpm as well but the exhaust drowns it out. It is more noticable when the car is warm, and my wild *** guess is that the lube in the tranny is thick enough when the car's cold to quiet it down.

No problem. I just went out to check the oil level, which is still over the halfway mark. Looks like it needs a new drive belt, though. I saw a couple of spots where it's fraying.

I started up the car while it's 86F out in the parking lot. No weird noise (no clanking noise on start up either), lightly revved it up a little to about 3k rpm, nothing unusual. Oil pressure is around 40-60 PSI while warming up.

The only times I can remember hearing this noise is at low speed like cruising in the neighborhood in 4th or 5th. This morning, it was when I was making a left turn. The noise was brief as I feathered the clutch out to get the car moving, and that was it.

that post sounds a lot like the transmission sound. if anything, perhaps familiarize yourself with the transmission sound by inducing it intentionally.

with all fluids up to normal temp, put the car in 4th or 5th gear, get down to around 1900 RPM. with windows down and no background noise, give it 3/4 throttle or more for a few hundred RPM... you will hear that sucker roar.

youre absolutely correct, the warmer/thinner the fluid, the more prominent the sound is. when cold starting, you usually dont even hear it.

i dont know the cause of the sound since i have never gone inside these transmissions. since it gets real bad when the dual-mass OEM flywheel is removed, I feel like its a something related to some slack in the trans, perhaps something they leave looser in high performance oriented transmissions to leave room for greater heat expansion or something. lol i have no idea what I am talking about though, I will ask my buddy who builds transmissions. i honestly never focused much attention to them.

Yeah, it's not a happy noise. I thought it was broken the first time I drove it after the clutch and flywheel went in. I was expecting noise, but not that much.

There's a user here who mentioned something about there's no spec for end play in the transmission, and that's what we're hearing. I don't remember his name, but he's a Nissan tech or something like that. I can live with it, considering how well the tranny holds power.

Brief? Probably not the girlfriend or wife in the passenger seat. >.>

Its your halfshafts that need lubing...AGAIN!

If you wiggle the stick in neutral, it sorta makes a similar clunking noise.

I looked up YouTube vids, it doesn't sound like a squeek. The noise I hear is intermittent at low speeds.

[EDIT] Found some videos of flywheel chatter at low speed. Very familiar especially with the G35 (with aftermarket clutch and flywheel):