I agree with everyone so far. I would first check the prop balance, then the crankshaft for axial play. I did have a prop that was so whacked out of balance that in time my firewall started cracking at the joints and things started loosening up. But it wasn't right away, it started happening about the 3rd or 4th flight in and I started not liking the way my airplane was vibrating on the ground at idle. Not to mention, that God Awful vibrating sound it made in flight.

I re-Epoxied the joints, re-fuel proofed the firewall and re-balanced the prop and it solved my problem. ( Thank God )

I hope your problem is as easy to fix like mine was.


Best of luck,

Pete