I have a 1993 Hunter 33.5 with a yanmar 3GM??, I believe it s 28hp. I developed a small vibration at 2200 rpm or above when transmission is in forward gear. The vibration does not exist at full throttle with transmission in neutral or in reverse. Cutlass bearing has very little play, no fishing line or any visible obstruction at prop, shaft looks straight, prop is stock two blade. Any thoughts?? Thanks.