I have a 2000 mercury 200 EFI, 0T100528 that has developed a "clunk" in the motor/lower unit, I got it out for the first time last weekend and I noticed when I put it in gear and was idling out it would make a kind of clunk sound every three or four seconds but would stop after a minute and when I got it up on plane no problems or weird noises. I tried to rev up to get on plane once before it was still doing its clunking thing and it sounded like it had half slipped out of gear and like the teeth were not engaging on the shaft. Im not sure whats going on, any thoughts?