First, let me ask if you have the OEM Flywheel. The OEM design is a dual-mass flywheel that helps with gear chatter. Aftermarket lightweight flywheels are better for performance, but will transfer the driveline pulses to the tranny and make the gears chatter more.

The sound makes the $40k car sound like a big rig...

I would have it checked out as it could be a bearing associated with the clutch. The fact that it goes away when pushed in typically would not indicate this however. The can be anything from normal transmission noise especially if running an aftermarket flywheel and or clutch combination or it could indicate something like a pilot shaft bearing problem.

Perry

Happens with all 6MTs on our cars.

Hard to state that his sound is normal without hearing it personally. It very well be that he has the normal manual sound but it may also be that he has a problem with something like the pilot shaft which goes away when the clutch and therefore the transmission is disengaged.

Perry

This sound is ubiquitous, Perry. I know you like playing devil's advocate and swooping in with some amazing alternative, but realistically, the chatter sound is well known for just about every 6mt G and Z owner. If you'd like, please search through some of the old threads and you'll see extensive engineering level discussions on the cause, design flaws, and what can aggrivate the situation.

OP,

I've had 2 aftermarket flywheels in my G and know the sound well. My understanding is that the OEM flywheel will also begin to experience this over time. I'd venture to say that the springs in the dual-mass flywheel begin to loose their "elasticity" and the chatter begins.

F/S:G35/350Z/FX35/Altima Grounding Kits

Quote, originally posted by Mr1der »

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Certainly there is an issue with the transmissions, however regardless of make of car transmissions do develop issues based on wear. My 67 Cougar certainly wasn't an Infiniti, however it certainly started to have transmission noise due to pilot shaft bearing wear. I also have had many, many manuals that had clutch throw out bearings that would rattle as well.

While it most likely is what is considered normal for a used Infiniti, it could also be an abnormal problem that should be looked at. None of us can realistically diagnose a problem without looking at the vehicle in question.

As far as an amazing alternative, what I mentioned is not amazing at all, in fact is very, very, very, common on older manuals regardless of manufacturer, especially those associated with a high performance vehicle.

Perry

In some cases, the sound develops even before the OEM Dual Mass Flywheel is worn out.

Could be since no one here as the ability to actually personally hear the car. It could also be the pilot shaft bearing, or like the experts here think, the normal manual transmission sound.

Perry

And you may be correct in your online diagnostic routine.

The fact however is that it can be several other things as well since you are not at the auto to diagnose it.

I do not have to search through any forums to know that the manuals can and do make noise.

I don't have to search through forums to know that I have also replaced many throw out bearings in my 40 some years of working on autos.

I also do not have to search through forums to know that I have also replaced many pilot shaft bearings in my 40 some years of working on autos.

I also do not have to search through forums to know that while a throw out bearing can go for a long time without getting replaced that a pilot shaft bearing can soon end up being a costly mistake in not replacing it before it can cause major avoidable damage to the rest of the transmission.

And one thing I have learned working on cars is that it is nearly impossible to diagnose with any degree of certainty a problem with an auto without having any physical contact with said auto.

Perry

Not too terribly unusual for the throw out bearing to rattle and not too terribly unusual for you to never have to replace it.

His may be a somewhat normal noise for an Infiniti or it may be something that needs fixed to prevent some major problems down the road. From afar we can't tell.

Perry

Also let me say that just because you take it to a dealer for work, doesn't mean they know everything...When I had my aftermarket flywheel/clutch installed during a transmission replacement, they ordered another transmission after putting the car together and it made the rattle. After the second one did the same thing, they said that's just how the car sounds...

After that, I called the performance shop where I purchased the lightweight flywheel/clutch to see if they had heard of the problem. They said the reason for the sound is that the 6MT has beefy gears and a thin trans case, which was a trade-off to save weight. The dual-mass flywheel is used to help smooth out the engine pulses and thus help reduce the transmission gear chatter.

If you think about it, when you engage the clutch, you disconnect the link from your engine to your transmission. In neutral, nothing is spinning until the clutch is disengaged (up). This spinning of the gears.

Here's a pic of how it works (not our car specifically, but you get the idea:

For more info, check out the car maintenance bible: http://www.carbibles.com/transmission_bible.html

You may be 100% sure it is not the throwout bearing on your car but you would have a hard time being 100% sure it is not something other than normal noise on otaku1010's car unless you happen to be Merlin.

What should occur if it is a pilot shaft or otherwise transmission related is the sound should tend to wind down slowly when you disengage the clutch (uncoupled). As mentioned earlier in my post I would not normally think it is a throwout bearing due to the noise going away when the clutch is disengage unless it is sitting loose in its fingers.

If concerned I would take it into Infiniti as if it is a pilot shaft bearing it could make a resonably cheap fix into a very expensive fix.

Perry