Once inside the clutch cover there's a plug that sits in the centre of the clutch assembly - it should be intact and in place rather than floating around inside, that's the first check point.
Taking the plates out and measuring the total stack height and comparing to the manual specs is also easy, assuming you have access to a micrometer or equivalent. Genuine plates are cheap if I recall, should they be out of spec.
The 'fingers' of the clutch basket are, ideally, smooth. Very slight grooving is acceptable but scores are a sign of wear. It's very easy to tell, a visual inspection or running a finger over them type easy. Gentle filing is fine but much material removal will lead to a rattly clutch. New baskets are expensive.
If all the above checks out then removing the basket (a bit awkward as the holding nut is is tightened to a high torque, pulling the bike along or over is very possible) and inspecting the springs embedded in the back is next. My springs had large gaps between them and the basket back so I bit the bullet and had them tig welded to the basket at their 'push' end. (On the basis that if it didn't work I'd buy a new basket.) Once re-assembled my clutch has been quiet and perfect in operation for 6000 miles or so. I fully appreciate that this is a fairly drastic solution and not for everyone, but it worked a treat for me.
Reassembly is straight forward enough (the time honoured 'reversal of removal') except re-torquing the basket bolt gives the same risks as removal and I found locating the pivot arm in the cover correctly fiddly and awkward, it took me several attempts before I was satisfied that it was right.
Also bear in mind that cable adjustment makes a massive difference. Genuine cables work well, after market cables are pretty useless, I put this down to four right angles between the lever and clutch housing.
Hope this helps.
