In replacing the drippless shaft seal on our '79 Tollycraft 40 diesel it was found that the engine mounts and compressed a bit and the shafts were actually touching the shaft log
. Not sure how many others have had this. I guess normally you'd just crank up the mount but on the Tolly its actually a big hassle as they have custom low profile engine mounts (of course they are not available) so the engines (3208na) had to be shimmed up. Luckily the mounts themselves seemed ok when removed, the rubber was intact etc. Replacing them would have been extremely complex.
I have to wonder how much noise was being transmitted due to this, my guess is that this has been going on for years. Previous owners had added multiple layers of sound insulation to the engine room, I have to wonder if they were addressing a symptom, not the root cause of the noise (besides the fact that 3208s aren't the quietest thing in the world).