03 g35 sport 6mt. the car developed an vibration all of a sudden. its like something out of balance in the transmission. clutch maybe

 

Have you had the tires balanced? The clutch won't typically get out of balance although it can shatter and blow apart the bellhousing, if the vibration is directly related to vehicle speed but the tires check out then I would suspect the carrier bearing on the propeller shaft.

https://www.z1motorsports.com/drives...ng-p-4110.html

It's really easy to diagnose, jack up the vehicle and grab the propeller on either side of that bearing and try pulling it up/down/left/right (not forward/backward towards the transmission-axle). There should be zero play on the bearing, when they fail it's usually the rubber encasement damper erodes between the actual bearing and the bolt flange, sometimes the wear is so severe you can tell it's failed just by looking at how torn the rubber is.

 

Yesterday I finally get to try the arc launch control feature at 4k rpm, I noticed after doing that, the car started vibrating and shaking during idle. I suspect something from the drivetrain broke, car idles normal, no vacuum leaks and car still drives normal.

I did quick google search found a thread from my350z suggesting changing the rear diff bushings. I am unable to visualize the rear diff bushings on mine due to RAS blocking it, also I don't see signs of fluid dripping from the bushings or maybe it did long time ago since car has 160k already. I'll need to jack the car to take a closer look.What could it be?

 

Start at the engine and work your way back, does the motor rock around in the engine compartment? Definitely sounds like a failed bushing or mount somewhere along the drivetrain. Probably easy to identify once the vehicle is up on jackstands though, sometimes it's as simple as an exhaust hanger but if the vibration is significant at idle I'd suspect motor mount, transmission mount/bushing since the driveline and rear end are stationary at idle.

 

I tried sticking my finger to the diff bushings and felt some ripped rubber in there. This is the best pic I could get.

Now to decide which bushings whiteline or spl?

Sorry OP, don't mean to jack your thread but hope this will give you ideas.