I have a niggle, there is a slight mechanical noise from the clutch end of the gearbox casing, stops when clutch is depressed, its not loud but it is detectable by my ageing ears.

I have read on several bike forums this can be pretty normal, is this so ?

most bikes do it

Sounds like the normal mechanical noise from a Busa clutch!
Nothing to normally worry about, depending on the vintage of the bike, there's added racket from the ramps on the slipper, etc. There's a solid centre available to cut out other chatter.... I wouldn't worry about it, but then I don't tend to.
There are some extremes, my 955i makes so much mechanical noise you can't hear the exhaust, and yes, they all do that.
Anything in my bike clutches that've heen dodgy have led them to normally quickly explode or slip to oblivion, with evidence found in the oil before, during and after the event..... a GSXR1000 clutch basket making a bit for freedom makes one helluva mess.....