If the noise exists when the car is idling, with the clutch released, but it dissapears when the clutch is depressed, then it might be a gearbox noise.

With the gearbox in Mexican Overdrive [neutral] & the clutch untouched, the input shaft, the cluster, & all the constant mesh gears are rotating. When you depress the clutch, all the rotating parts come to a stop. This is when the noise stops.

Do we see a connection here.