Starboard side where it could be a cable up against the hull? My old boat had some common rattles at the transom panels and the motor throttle cables.
Port side half way up. Curious what the dealer is going to say, because it’s got to be a crazy amount of work to figure out what it is. I’ve tried blowing air in the areas I could, but it won’t move. Was hoping it would work its way to the back and be able to be taken out.