I recently noticed a knocking sound coming from the engine while cruising. I dropped the lower unit and found no water in the gear lube (it was deep blue in color). I did, however, have some metal shavings on the drain plug. I've read that some shavings are normal but I'm not sure what would constitute too many. I went ahead and changed the impeller and replaced the washers. I ran the engine with water hose attached, and the lower unit is still making a knocking sound. A couple of years ago I hit something with my prop and had to have it repaired....it was slightly bent. I haven't had any other problems until recently. I was running at full speed when I first noticed the sound and it was at first a random knock. Based on what I've read, it sounds like I could have a bearing that's gone out or maybe a gear issue. I would like to take the boat out this weekend to see if it is still making the sound at full throttle but I don't want to make the issue worse. Any advice?