Heavy Vibration

[i4110peter]

Went out Thurs, got boat up to speed, and I think something let go in the outdrive. Still goes into gear but vibrates so badly it's scary! I just had the gimble bearing replaced in March of 2015 and don't have many hrs on it since then. When engine is running in neutral, very noisy in outdrive but no vibration.
Any ideas? This is the mercruiser outdrive with the 165 hp straight 6. Thanks for any input.