Boat is an '87 with a 3.0 omc cobra. Last fall when I was winterizing it I could hear a knocking noise coming from the lower unit. What's strange is, while standing next to the boat, I couldn't hear anything, but from say 20 ft. i could hear the knocking. Gear oil was up to full level. Last spring I replaced the u- joints so I don't suspect them. It's definetly not an engine knock. Any ideas?
