i had a weird buzzing noise as well although with a Tenere...one at certain revs/speed combinations... Couldn't figure it out for ages! Thought it was the springs inside the WP forks vibrating or something... Took apart the dark/headlight.. Looking for something loose!
In the end it turned out to be the chain! I had been running it a bit on the loose side... Adjusted it to manual specs ( 50mm play? ) and noise gone!