What's this strange transmission sound when I am at idle wit

What's this strange transmission sound when I am at idle with the clutch out in a 2000 Mitsubishi Eclipse GT?
Hello. I have a 2000 Mitsubishi Eclipse GT. When I am at idle and the clutch isn't pushed in, it makes a strange "transmissional / flywheel" rattle / rubbing sound but when I push the clutch in, it goes away and the car is idling calm as a mouse. The car drives and shifts perfectly, the clutch feels perfect. Is this something serious I have to looked at or is it nothing to worry about?

Ok, when you push the clutch in the Input shaft that goes into the transmission will stop turning, this shaft has the clutch disc splines and disc on it...when in neutral and your foot off of the clutch the input shaft is turning at the speed of the engine idle and often the gears in the transmission turning yes they'll be turning may be heard...the most comon problem is a worn input shaft bearing..

if you feel something strange, then somethings wrong with it. take it to the shop before its late.

your throw out barring is going out.

Yeah this sounds like your throwout bearing going bad. The part is comparatively inexpensive, but youll have to drop the trans to get to it, no small job by any means. The bearing should run under $100, but the labor will be high if you can not do it yourself. typically they are replaced with any clutch for that reason, they are cheap enough that its worth it to save yourself the possible trouble of having to pull it separately again. When you push in your clutch it goes away as the shift fork is putting pressure on it, making it tight enough that it can not rattle like that. Get it looked at soon.

River rat is correct. If the sound is with the clutch out, it's either the gears spinning normal, or the input shaft bearing bad . The throw out bearing could only make sound if the clutch is pressed..it does not turn with the clutch out.