rattle and vibration at 12k rpm

[damz]

while riding my rvf and hit around 12kish it makes a lot of noise and vibrates quite a lot, after 12k its fine and under its fine, its just in a very narrow band of the rev range.

any idea's what would cause this?
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Current Bikes RVF400 - 94
Cars: RX7 FD, Eunos Roadster
Former Bikes: FZR 250R 89, ZX7R 98