Weird noise at idle when the clutch isn’t engage, past owner just replace it
 

I just got my Z yesterday and the car sounds like a v8 when the clutch isn’t engage, I don’t think it’s rod knock because it goes away as soon as I step on the clutch.

sounds like he put in a lightweight flywheel.

does it sound kinda like a cement mixer?

It sounds like old v8 engine
 

it sounds like a diesel truck or like a old v8
He put a Jim wolf clutch and flywheel

so it is a lightweight flywheel, i bet it is just chatter. post a video

^^^ What Trav said. Lightweight Flywheel = Transmission gear lash/chatter. Specifically at low RPM (<1500) while under load. You can minimize the noise by keeping your RPMs higher when shifting. Lugging the engine is never a good idea in any case, but with a lightweight flywheel it will sound like your Z is about to fly apart.
-Icer

Uploaded a video
 

I posted a video already, here is the link

This is normal. You're hearing the clutch throw-out bearing. Simple test; push in the clutch pedal while listening, does the noise immediately go away? If so, noise confirmed. All 6MT 350Zs make this noise while idling in neutral with the clutch released. The bearing noise will get louder over time. A temporary fix is to replace the bearing while also replacing the clutch. If you're clutch is old/worn go ahead and take care of it, just understand that even a new bearing will start making this noise after a few weeks or months of use.

Note: If you're running with a Lightened Flywheel, the noise will be a little louder. This is because the combustion pulses through the crank aren't being absorbed as designed/intended by the heavy OEM dual-mass flywheel. This won't harm your engine or transmission, you just sacrifice some comfort (noise & vibration) for performance.
-Icer

You can diagnose the noise you describe by putting the car in neutral, and depressing and releasing the clutch pedal.

• If you hear a growling noise when depressing the clutch pedal while in neutral and the noise goes away when releasing the clutch pedal, the throw-out bearing is worn.
• If you hear a noise when releasing the clutch pedal to engage the clutch while in neutral, but goes away when the pedal is depressed, you have a bad transmission input shaft bearing.

You said:
This is a symptom of a bad transmission input shaft bearing.

What year is your 350z?