I have a 87 cobra outdrive that I have kept garaged for 2 years (untouched). I replaced all fluids in motor and i/o. When I took out the boat yesterday It seems to have a rumbling noise I have never heard. It happends at idle an low rpm seems to go away with higher rpm. Sounds worse when trimmed and when I turn port or star. No loss of power or engine performance. I'm thinking universal joints??