Took the boat out last night and noticed a vibration in my cabin as I was underway. Cut the trip short due to this but by the time I got back if I was above 2000 RPM, the whole cabin was vibratiing. In addition, the vibration got substantially worse if I increased RPM.s Wheel was straight forward. Would a U-Joint cause this? I don't think there is anything in the prop or wrong with the prop. They are Volvo Penta Outdrives with 5.0 L V-8's. Only the Starboard motor is doing it.

Thanks!