PhilAddison wrote: All rotating equipment has a critical speed. This is the point at which vibration is at its highest point. This is normal, but is not good to run in this range. That is exactly correct, and if you call Merc they can tell you that rpm. But I am betting it is your engine cowling, my buddys did it too bad at 3000 rpms. Spray some wd-40 on your cowling mounts, then run it, if it isnt as bad, then you found your problem.