my 2008 will "buzz" at certain rpms. occasionally while warming up below 2000, always passing through the upper 3000's, always ABOVE approx 7000 rpm. always been that way. no course vibrations, no significant fine vibrations otherwise at other rpms, and has nothing to do with gear. this is just for your reference. as it's a used bike, and you tightened fasteners/bolts, might be good to give it a good go over checking all the service basics that might make it run rough (plugs, oil/filter, air box/filter clean, valves, old/bad gas, TB's, etc. unfortunately, just because someone says the work was done, doesn't mean that it was REALLY done. years ago, i caught a popular mechanic in our town simply blowing out our car's plugs with compressed air, putting them back in, then charging us for new plugs! not so many years ago, i went for the first "free" oil change/service on my new car. when i got home, it was the same old oil and dirty filter. the guy penciled his work. sucks. you have to be careful.