Originally Posted by JKBall
Sorry for the delayed response.
Yes. In neutral and stationary, the noise is present. Yes, again. Enough pressure applied to the clutch stops the noise but not enough pressure to release the clutch completely.
OK. From a troubleshooting perspective.
You have pinned it down to fewer moving parts. Those attached to the gearbox side of the clutch. (Because it occurs when you are not moving.)
Now the moving bits are the throw out bearing, (no pressure on it), and the input shaft to the gearbox, (shaft, bearings, seals. The pilot bearing only moves when the clutch is fully disengaged and there is rotation between the flywheel & clutch plate.)
Given that the clutch does not need to be fully depressed to stop the noise, that would seem to indicate the ToB, as the noise goes away once pressure is on it, but not enough to disengage from the gearbox input side, (so it is still moving, but now no noise).
My ToB failed last year. In my case, it was quiet, until I put pressure on the pedal, then it screamed like the gates of Hell had opened under the car. LOUD! (You should have seen the face on the cop pulling into the shopping center carpark who had stopped there and was next to me as I was coming out & had to stop before entering the street!
) Mind you, that was, as far as I know, the original ToB, at ~80,000km - 150,000km old. I got the JK 2nd hand & the PO might have had it done in the 70,000km they had it.
Your sound is the opposite instance. Where my ToB seized and was scraping the pressure plate fingers & wearing them down. By the time I got all the parts in, it had worn through most of them. And the ToB itself was also worn through.
Throw Out Bearing
That loose bit is what is supposed to apply the pressure to the fingers...
, and that is all it is, would be that the ToB may be tightening up and rubbing a little on the fingers, but as soon as you put pressure on the pedal, the friction between the fingers & ToB surface overcome the tight bearing & it turns normally. The slave cylinder piston is spring loaded, so that a slight pressure is always applied to the ToB so it always remains in contact with the pressure plate fingers.
Or, given that we have not heard your JK, in particular, to compare, it might just be the normal noise of spinning bearings as the mechanic said.