Sounds like the clutch plates are/might be doing a slip, grip, slide on the clutch casing. Often you notice this kind of thing when you change oil or use a different brand of oil.
Some bikes are very prone to it, Triumphs and Yam R1's spring to mind though I think they were just imitating dry clutches and pretending to be ducati's
It probably isn't anything dire, though I'm sure someone will know better and let you know it's some kind of mechanical death rattle
Make sure that the oil level is good as this can have quite an effect on the clutch.