above 6k my bike has extremely excessive and intrusive engine vibrations and a loud reverberation noise from the engine area. any ideas? under 6k its fine. it vibrates enough to cause discomfort and the vibration noise is louder than the engine noise.

Something not tight - so have you had a look?

Airbox?

Will it actually rev past 6k? If not, check and make absolutely sure that the carb rubbers are fully seated both to the head and the carbs.