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There is usually a damper plate between the engine and the gearbox. This special plate with springs or plastic cams is mounted on the flywheel and serves to dampen torsional vibrations of the engine (especially at low revs) and to slightly absorb the impact of engaging the gearbox. If there is a rattling noise (which was not there before) from the clutch housing at low engine speeds, this usually indicates a worn muffler plate and not a defective gearbox. Loose or broken springs are causing the noise. It is for a trained ear to determine whether it is a defective muffler plate or whether the "hammering" of a worn gearbox is audible. As the clutch heats up, the sound will change. Not if the damping plate is defective.

Damper plate with steel springs.   Damper plate mounted on the flywheel.