Knocking noise

Hello, I have a 1974 Correct Craft Martinique, and last weekend, after running over one of my lines and wrapping it around the prop, I noticed a knocking noise coming from the rear of the boat, and it sounded like it was coming from the shaft that holds the propeller. The noise didnt start until the day after this incident happened, however, and it went away a few times but came back again. My father and I believe that it is coming from either the transmission, or the actual shaft, but it sounds to me like it is coming from the actual shaft (noise does travel, though). We have checked the prop, and it is secure in place and shows no damage. I only hear the noise when I am moving, and only when I am at idle speed. Also, the rope seal seems to be leaking more water than usual. Any help would be greatly appreciated.

You shouldnt have any damper noise especially if you had none before. Did you check the strut to see if its bent slightly? Alot of them will bend and not be 90 degrees with the hull. Also, does it seem to vibrate at higher speeds as compared to before? Sometimes you can tweak a prop blade. See if the prop shaft spins freely. I hit a small log at idle with my mustang 17 (almost identical boat to yours) and it tweaked the strut. I had no noticable vibration, but my damper springs were going wild. I had a fair amount of resistance to turn the shaft as compared to before. Put on a new strut, realigned, and problem solved. Dont bring the idle up to correct this, its better for the clutches to engage into gear at lower rpms even though they can take it.