Hi all I have a 1981 Hunter 27 with a Yanmar 1GM10. I finally got her in the water last weekend (I know, I know) and drove her with the mast down from the boatyard to the harbor, an approximately five hour trip at approximately 3200 rpms, with no problem whatsoever. I raised the mast the following day, and the engine subsequently began making a periodic thumping noise at rpms above 2000 in forward gear. The frequency of the thumping is less than the rpms, and the prop and shaft are clear of obstructions. The thumping only occurs when the boat is in forward gear (no thumping in neutral at high rpms). I've watched the engine, and can't see any obvious vibration or movement correlating with the thumping. This has been a periodic problem with this boat. Any ideas? Motor mounts maybe?