I recently purchased a Mercury EFI v-6 150hp. outboard. I have about 20 hours. I am very happy with it's performance thus far. It runs well. The only thing that seems odd is after I have had the engine at higher speeds and I decelerate quickly the engine makes a metalic knocking noise that sound like there is something loose in the engine. Or maybe more like knocking cylinders. It is not noticable unless you are listening for it. Although I did see my Father-in-law look back at the engine when it happened once. It may be just how the new engines sound. I followed the proceedure for break in for the first 10 hours. I didn't run it at full throttle and I varied my speeds. I am paranoid that I have done something wrong and have ruined my new engine.Is this sound typical?