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):

If you are getting the clack when you push the throttle or let off at low speeds or high tq conditions then its the halfshafts I suspect. You need to video the episodes you are having with your car.

The intermittent chatter in the 4th clip is as close as it gets. I drove home and to a friends house after work, and all was well. I guess sometimes I nearly stall the car from getting it going at really low revs, so that noise is brief. Same when doing the clutch slip test in 6th after abruptly releasing the throttle. Gosh last thing I want to hear is rod knock.

if its a single clatter then it is halfshafts, if not and its multiple clacks so to speak then it is something else.