My '04 has done it since the day I drove it off the lot with 7 miles on it. 48k miles now and the noise is no different...just something you have to get used to...

You could probably eliminate/reduce it by bumping your idle to 850 or so, that pretty much got rid of mine after I went TT.

 

I hear it when I turn the radio on: the sweetest sound! I had a new ACT flywheel and a pressure plate and clutch placed with a brand new transmission also, the car drives pretty fast and the sound is pure nissan 350z. I love it!

 

awesome, im gonna wait a while before i change clutch/flywheel. i dont see a point in it since i only have an exhaust right now.

 

I hate that about 350Z.... they used the same transmission on some of the infinity models (G i think) it's one of the loudest transmission set up made today... XD you'll get used to it.

 

It may not be the throw out bearing at all, i've been having the same problem in my 06 coupe with 37,000 miles. I took it to Nissan and came out of pocket for a new throw out bearing, got the car back and it was still doing it so i took it back and this time they replaced the transmission.
I've had it back for about two weeks now and was in the drive thru the other night and noticed it was still making the rattling sound so as you can imagine i was pretty frustrated at this point, so for some reason i happened to reach down and turn the air off and the rattling stopped, turn it back on and it came back.
So now i'm wondering if it could have something to do with the A/C clutch but either way i cant believe Nissan couldn't diagnose the correct problem and just decided to throw a new tranny in it, not that i'm complaining!!!
So before you do like i did and waste money on a throw out bearing go outside start your car put it in neutral and when you hear it grinding turn the air off and see if your's stops as well!
Good luck

 

This is odd, my first throw-out went 100,000+ and no noise, the new one went 5,000 before starting. Bad QC.

 

I put in an ACT clutch and flywheel and as expected i got over the added tranny noise from the flywheel, car has 65k miles, and this rattling noise just started to happen about 3 miles after the install. It happens when the clutch is engaged but mostly when im in low RPMs or not on the gas at all, no noise when I'm not in gear rolling. But good lord its getting to be quite obnoxious.
How loud is what you guys are hearing? Its sort of embarrassing to be driving next to someone and have a really loud rattling emanating from the bottom of my nice looking car.

 

You removed the only thing quieting the pulses coming from the engine running. The engine firing pulses make the input/mainshaft of the trans rattle. It's going to happen with a single mass flywheel. However, the lighter the flywheel, the louder the rattle.

 

Apparently this is not just a Z problem. I have the exact same problem with my 6spd Frontier and have also been told by the dealer its normal. Started at maybe 5K and still there at 29K, no difference. It does get annoying sometimes. But I feel better knowing most of you guys have the same issue and that its not a big deal.