Mcneil, I'm using balsa from one of those supermarket planes, then laminate it with scotch tape. This is how I move the motor forward. Take a razor blade and trim the bottom of the mount. On two there was a bit of extra foam there. If the motor is not snug against the mount I would suspect this problem. On one even when seated all the way back it still had to much clearance. I cut the required amount out and reseated the motor. good luck, tim