I had that!  Motor mounts were shot... you could literally stick your thumb under forward P mount when you throttled up!  Also PO had a 3 blade feathering prop that had some bad bearings.  Replaced motor mounts, prop shaft, cutlass, and new fixed 3 blade prop and she is now smooth as a you know what!  You may or may not have all that going on but we figured either the prop bearings went bad and worked its way on the rest or the motor mounts went and worked the other way.  Not sure if the prop shaft was actually bent but it was pitted anyhow so figured good time to make it all new and will last as long as we have her!  Good luck! 

At idle it was very obvious yes but could tell also as I idled up it was not as smooth as should be.  Remove your engine enclosure from Galley and start engine at dock.  Have someone throttle engine up while you are watching and you should see movement caused by the torque from engine.  Like I said you could literally stick your finger under (didn't do that fyi) the mount when idled up.  You should also be able to man handle the engine to get a feel for how secure they (mounts) are.  The engine should have slight give from the rubber in the mounts but not move more than say 1/8" or so.  A qualified Marine Mechanic would probably be recomended if any of that looks suspect.  Kinda like reefing... prob should reef the first time you wonder if you should reef.  You prob should call a MM if any of those tests raise a Q!

I bought my 2004 Catalina 36 MKII with the M35B Universal engine when it was only 2 years old and it seems I have always had excessive engine vibration and noise.  The noise level actually seems to be worse than the vibration and I've often wondered if my noise problem is actually other parts of the boat vibrating and making the noise from the engine vibrations and not the engine itself.  It seems like the most noise is coming from under the refrigerator and I am suspicious of the water muffler making the noise.  I have never examined the water muffler.  There is no question the noise (and the engine vibration) is worse at low idle, but I need to be above 1,000 or 1,100 RPM to reduce the noise and vibration and it still seems excessive at higher RPMs.

I'm sure many owner have heard cockpit storage covers vibrating at certain engine frequencies that are loud but go away at different engine frequencies or if you weight down the covers.  It sounds like there may be equipment under the galley refrigerator that may be doing the same thing.  Any ideas / info / or experience with something like this?

I am going to check my engine mounts.  I have checked my alignment to prop shaft and it checks out, and my noise problem does not seem to be tied to being in gear.  I may also try to examine water muffler, as I have never accessed that portion of my boat.

Thanks for any info or advice.

Update - There are four screws securing the Aqualift water muffler base to the boat.  One of those screws was not snug.  I cannot believe the difference that this made.  The main source of noise at engine RPM around 1,000 was not my engine -- it was a vibrating water muffler making lots of noise.  If you have loud noise bothering you CHECK THE FOUR SCREWS SECURING THE AQUALIFT WATER MUFFLER to see if that solves your noise prooblem!

Thanks for posting your findings. It helps all the rest of us.