I have the same problem . It starts at 4100rpm and stops about 4500. I think hyosung should do something about this befor someone gets hurt from it.I was doing 45 in a turn and the vibration shot me in the other lane.This is the bikes only flaw that I see so far I only have 400 miles on it and if they don´t fix it, I will sale it and get a GSXR.