Originally Posted by RedDog

Find a quiet, straight stretch of road and when the buzzing/vibration starts, hold the screen with your hand, then try the fairing in various places, then the clocks.
Try holding each part of the bike you can safely reach in turn. When the buzzing stops you have found the loose part.
Trial and error really. As above, the screen on my XTX also vibrated, a small rubber washer under the screen cured it.
Could be a loose mudguard, fork shrouds, radiator etc. Shouldn't be too hard to track it down.