i have a 10 lb. flywheel it shifts well too

 

If it's your cv joints it would be vibrating only when you really get on it. (also when you put the clutch in it will stop.)

here's the TSB on it:

https://www.s2ki.com/stor/library/TSB/A02-063/index.htm

could this be clutch buzz? clutch buzz also goes away when you put the clutch in. here's that TSB on it:

https://www.s2ki.com/stor/library/TSB/A00-054/index.htm

 

I have a lite flywheel and i have quite a bit of cluch buzz at these same rpms. if it feels okay and shifts good, drive it. the buzz just takes some getting used to it.

 

its not cv joints those were replaced when i got a brand new prop shaft my buddy took a ride with me yesterday and said it sounds like flywheel it only hapens during decceleration when i give it gas it completely goes away the buzzing hapens around deccel 2.5 to 4.5 it varies. second and third gear are torture in school zones or any where with 25 to 35 mph speed limit. if i let off the gas buzzzzzzzzzzzzzzzzzzzzzzzzzzzz buz buz