I've had my H30 for about a year now without major problems, but last week something bad might have happened. I took her out of the slip, put it in forward and immediately observed significant vibration at about 1500 RPM. Increased the throttle a little, and vibrations increased significantly. Turned around and headed back to the slip, when suddenly everything was fine. No more vibrations, so I turned around went sailing. The vibrations did not reappear when I brought it back in at the end of the day.Now I'm worried that the prop will fall off next time I go out. Does this sound familiar to anyone? I'd prefer not to haul it out to get to the source of the problem if it isn't necessary. Thanks for any suggestions on where to start looking.