Hi, new to the forums and I know there are endless discussions on this topic but I have yet to find an instance with my specific symptoms. I have recently purchased a 2008 g35s 6mt sedan 90,000 miles. I know everyone says the car has a loud transmission but I'm getting a rattling sound coming from the center of the car (where the tranny should be) at idle but It doesn't always make this noise. One thing I notice is when I press the clutch in it goes away immediately. I've seen this issue all over the forums but herd nothing about the idle rattle going away on its own sometimes (without pressing the clutch).

 

Flywheel rattle...? My shaved flywheel rattles here and there.

 

the car is completely stock with original clutch. My concern is that the car isn't always making this noise at idle with the clutch out. Seems to be pretty random

 

It's just gear lash in the transmission. The intermittent nature you're observing is probably just related to the temperature of the tranny.

BTW, when was the last time the gear oil was changed in the tranny?

 

I just bought the car about a month ago so I'm not really sure, didn't see anything about it in the service records. Would flushing the gear oil help eliminate the sound??

 

Yeah, if the gear oil is old and cooked it will definitely contribute to the noise, so you might try changing it. Be aware though, it is the nature of the beast to some extent. Even with fresh oil, under the right conditions these trannys can still make some rattle; some more than others. That is why they use the dual-mass flywheel to try and dampen the impulses coming from the (relatively) harsh V6 attached to it. If you are sensitive to the sound at all, you want to be sure that when it comes time to change your clutch, you never go with anything other than a dual-mass flywheel.

 

I herd this specific car is loud and you hear everything. I've only had it for a month and I'm a bit paranoid plus I have never owned any nissan/infiniti prior to this one. Thanks for your insight. Much appreciated

 

Also just to throw it out there. It could be exhaust heat shield starting to loosen up and rattle.

 

yep, the 6MT has slight noise and vibration at idle. Mine does it. I read that G37s Sedan addressed this issue.

As long as the noise and vibration is not excessive, I wouldn't worry about it. And change out the transmission fluid is age is unknown, just a cheap insurance IMO.

 

Yea check the heat shield, i recently had a raddle, checked under the car (basically in line with the drivers seat) and one of the clamps had rotted out so i just took it off and replaced it with a hose clamp

 

Guys, an exhaust rattle wouldn't go away when you press the clutch in.

 

I apologize for not being specific enough. Rattle might not be the right word. It's more like the normal sound coming from the transmission gets louder. Maybe a little "rattley" but not the type you would associate with a loose heat sheild. It's not terribly loud but it's definitely not just the normal sound of the car. I usually notice it after driving for 10 or 20 minutes so I'm starting to believe it is just the transmission heating up. I plan on flushing the tranny fluid and most likely the differential while I'm at it.

 

Same issue here when I bought mine in Nov 2014. Dealership replaced tranny fluid and I can still hear it. It's super loud and embarrassing in heavy traffic so I just crank up the tunes

 

Update: so I've replaced the gear oil in transmission and differential, and at first I noticed a big difference and how my transmission sounded after some spirited driving. This lasted about 2-3 months before making the harsh sounding rattle coming from what I believe to be the transmission. It doesn't sound as bad as before and only acts up after driving somewhat spirited for 30 mins+. I've done research on general car problems and what came up isn't too promising. From what I could find, it seems like the problem may be my input shaft bearing. I have no idea how bad this problem is and how to go about fixing it. Should I act now or let it the bearing take its corse. Thanks in advance for your insight.

 

Joe, it's hard to know what the sound you're hearing is over the internet. As I originally mention last spring, it could still very well be just the "normal" gear lash that is inherent in these trannys, albeit some more than others. Gear lash noise will always be more pronounced when the gear oil is hot, which would coincide with your symptoms of only doing it after a 1/2 hour of spirited driving. I'm not saying it isn't possible that your bearing isn't making noise, but it is far less likely. If the bearing was so worn as to cause a "rattle", I would think it would be making the noise constantly, and not just after your 1/2 hour of spirited driving.

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