Knocking noise in gear

I,m getting a knocking noise when in gear on starboard side. Thought it engine at first but when in in neutral no noise I can increase engine speed in neutral and no noise. I looked at the V-drive and transmission and could neither see nor feel any vibration but could feel and hear the noise when in gear. This a 1990 350 Sundancer with v-drives and 454's. Any ideas?

Good chance you have a misfire on one or more cylinders causing the damper plate springs to make the noise you hear. when was the last time you had the engine tuned up?

Sounds like a cylinder miss or dead cylinder same exact thing happened to my 7.4 check plugs and wires if you raise rpm in gear a few hundred it will go away confirming the motor is missing 7.4 are very good at hiding problems

It is most likely your transmission and is very typical and not a problem. Every inboard I have owned exhibited this ratting noise What it is are spring dampers rattling. If you search this site, this topic has been brought up a few times. And you'll notice the rattling goes away as soon as the speed increases.

As mentioned above, your engine can be fouled or slightly fouled on one or more cylinders causing a miss.
Due a full tune up and see if it changes.

When moving in gear bump the rpms up over 1000. If the sound goes away, then it's one of two things. As mentioned above the engine has a miss which is heard thru the trany via the dampener plate or the springs in the dampener plate are slightly lose. Either way no damage is happening other than a tune up on the engine.

Does the sound sound like marbles in the trany. If so, it's normal for some to do this. Just bump rpms up a bit.

FYI, there really isn't much inside a trany to fail. Most of it is gears, shafts, clutch and bearings. Failure is rare, if anything is waring it would be the clutch, its abused by shifting at higher rpms or racing the boat up on plane via fast movement with throttles over and over. Like a teen racer.

Actually, the noise is due to a worn out our missing cutlass bearing on the starboard engine. Thanks to all the good folks who responded to my post.