Honda Dylan - Grating noise from Clutch/Transmission Area

Ok for starters, my bike has done about 35,000. Its an 04 Honda Dylan 125. I do regular oil changes, and the bike is running well, except for this current problem.

On a ride from Penzance to Sheffield earlier this week i noticed a grating sound coming from the rear end. I assumed at the time it was the variator assembly coming loose and grinding on the case. So yesterday i stripped it down and at the same time changed out the roller weights as im now living in Sheffield and i now favour more acceleration than a higher top speed.

So after doing this i took it out for a spin, and it hasnt fixed the noise. Ive narrowed it down to a speed range of between say 0-25 mph. After i hit 25-30mph the noise disappears. Through that process of elimination i think it can only be one of two things. Either the clutch or the transmission/gears.

It has happened once before, maybe 9-10 months back, and after a while (a couple of weeks) it just stopped.

Tomorrow im thinking of swapping the transmission fluid, to see if i can see any metal in it, which might indicate that things are going south. It was last changed about 10 months back, and according to the haynes manual is a once every 10,000 miles job. It has done maybe 6,000 miles, but i may as well do it anyway.

So what im hoping is someone has some ideas besides mine, or could confirm im on the right track.

Thanks for any help you can give.