850 GT boring noise

[tetarabra]

My GT is now finished . Happy but I experience a strange noise  . Must add I bought a non running bike. When hot after a few kilometers I face a clattering noise seeming coming from the gearbox and only when on the over run. Only job done on the gearbox was the change of the 3 bearings in the rear lid.
Odometer transmission checked afterwards and fine.
Any idea welcome 

[Don G]

One of the stands rattling on something perhaps? Also eyeball the exhaust system etc.  DonG