Clutch/transmission problem
When the car is sitting idling,and the clutch is not depressed,it makes a grinding noise because the input shaft of the transmission is being forced to turn by the clutch,which is engaged,and even though the trans is in neutral,the input shaft is still turning,and this is called "neutral roll over" noise,and some of the assemblies inside the trans are freewheeling around.The noise goes away when the clutch pedal is being depressed down,because the input shaft of the transmission is no longer turning.So it does sound like an internal transmission problem.It is still possible for the throwout bearing to be bad,and it can be checked when the trans is removed from the vehicle,Remove the throwout bearing from the trans input sleeve,and press down on the bearing flange and turn it at the same time.It should feel smooth and free.If it catches or feels gravelly,then the bearing is bad and that could be your noise.Also,turn the input shaft of the trans and same thing,if it's smooth and free or if gravelly feeling......Good luck.