If it is a sort of rattly noise at idle, and goes away if you try to engage a gear (NOT REVERSE!) without depressing the clutch, then it is probably the anti-shock springs on the clutch plate, these wear into the clutch plate over time and can rattle, and even fall out. The drag on the gearbox primary shaft when you try to engage a gear without hitting the clutch causes some load on the anti-shock springs, and stop the looses ones rattling. Don't worry about it.
Are these springs really unnessiary?