When we were going to take our 1985 Sea swirl 6 cylinder boat out yesterday from the time we turned it on we heard a clicking /knocking sound that was new. We were already out on the water but we didnt go out long and it actually seemed to run fine. The noise did not get any louder or anything. When we were back home we found that when we take off one spark plug boot on the one closest to the back of the boat on the driver side it totally goes away. We did have someone check the compression in the cylinders and they are all good. Also the temperature was never high and the oil is all good. Could it be like a bad spark plug wire making it make that sound? Or what might it be. Just would like to know maybe the order of things to look at if anyone knows. Thank you.