Hi..
Depends what u call a rattle, 1 mans rattle is another mans rumble.
If it concerns u, it needs stripping for a bit of inspection.
More than likely a wear issue, often the springs get weak in the clutch hub & rattle like crazy, this can affect most bike clutches, but could be the dreaded bung that detached from the shaft end, never seen it myself, but it does happen, I would have thought any foreign body rattling around in a clutch assembly would either lock the clutch up or stop it releasing.
Spanners out time.