I recently bought a 2005 350z with a vq35de, and have noticed when I’m accelerating below 2,100 rpm’s it makes a weird sound, but as soon as I get to about 2,100-2,200 rpms it goes away. Only happens when in gear and accelerating, haven’t noticed it happening much in first gear, a little in second, but it happens in every gear after that, and doesn’t happen when reving in neutral, anyone have any idea of what could be the cause of this? And if I should be concerned?

 

Sounds like someone put a light weight flywheel. Normal if thats the case. Any history of the car? like maintenance?

 

well the only thing I can think of that I know about that would possibly be related to the flywheel, would be it has an after market stage 2 clutch, so maybe when putting a new clutch on they also put a light weight flywheel on but I’m not sure

 

Chances are they did. Only way to find out is by dropping the transmission. Or maybe you can check it out through the inspection plate on the transmission. Although its probably too hard to really see the flywheel.
I just installed a clutch kit with light weight flywheel from Z1 about a month ago and I get that chatter/rattle noise at low rpms. You'll get use to it if not you can purchase an OEM flywheel for $1,000 or Z1 has a nodular one that is very similar to oem specs that wont be noisey.

 

I’m not worried about the sound as long as that’s normal, so if it is I’m sure I’ll get used to it eventually it just sounds concerning so I want to make sure it’s nothing to be concerned of if you know what I mean, where is said “inspection plate”?

 

inspection plate is where the transmission and engine block mate

 

alright well I appreciate the assistance

 

I watched some videos and it doesn’t seem like the sound from a light weight flywheel is quite right, it seems like that sound is present even at idle, and it seems like it’s more of a clacking sound, the sound I’m hearing is more of a uh humming or roaring sound that happens between 1,500 and 2,100 under acceleration only, so any other ideas on what this could possibly be?

 

Some lightweight flywheels will still make some noise at idle and not in gear.

When it's in neutral, does the noise go away when you depress the clutch pedal? Or does the noise change at idle if you cycle the clutch pedal?

 

there’s no sound whatsoever unless I’m accelerating in gear under 2k rpm’s, so no noise at idle, no matter what position the clutch is in, and no noise in neutral

 

On my car i do get noise in neutral and if i press the clutch pedal the noise goes away. This was already happening before I installed the new clutch. Only difference is the noise is louder. Just thought I shared this information

 

Humming or roaring sounds typically indicate a bearing issue, but could also be related to a failed bushing our mount. It's possible the noise you're hearing isn't isolated to the transmission. I recommend inspecting wheel bearings, rear differential, and your driveshaft. Fingers crossed it's not the transmission input shaft bearing. Rear wheel bearings on 350Zs are not uncommon maintenance items as they age, and the humming/roaring sound a failing rear bearing produces can be very loud due to the resonance and harmonics of the rear chassis and interior. Driveshaft failures on 350Zs are rare, but these cars are getting older. Universal joints can start failing and will be more prone to fatigue if you have blown rear differential bushings, transmission mount, or engine mounts.

In terms of bushings/mounts, I would check engine, transmission, and differential for signs of aftermarket parts or broken units . Do you have any idea what brand "Stage 2" clutch was put in? Any details or receipts/records for that? If it's a metallic or puck style clutch, there could be noticeable NVH changes and engagement behavior changes. I strongly recommend staying away from a solid or poly transmission mount for street use, those will cause a massive increase of NVH inside the vehicle. (Note: NVH = Noise, Vibration, Harshness).

Good Luck!
-Icer