454 Mag / Bravo 1 vibration
 

I noticed a vibration in one of my engine/drives over the weekend. They are 1991 Mercruiser 454 Mags(Carb) with Bravo One drives with Mirage 23P Counter rotating props.
I can put my stbd engine in gear, and run it up to 2000-3000 RPM, and it is smooth. But when I do the same to my port engine, I have a vibration I have'nt felt before. It is not there when the engine is in nuetral and rev'd up.
I have removed and looked at both props and they look fine. My next guess is the gimbal bearing or u-joint on the vibrating drive. Anybody been here before??
Thanks for any reply,