The noise you're hearing is a wiper seal (bushing) on the shaft in the lower part of the outboard leg. If you look under the engine pan at the front of the leg, You'll see a small opening that leaves a small part of the drive shaft exposed. This noise appears after the engine warms up. Alot of the dealers that sell Yamaha engines on boats but are not certified techs are not familiar with it. I discovered the cause on another forum back in '03 after brainstorming with alot of guys across the country. If you spray a lube like WD-40 04 silicone into the area until it runs down the shaft, it will quiet it. One thing to remember is to spray the area when you flush your motor after each use. The noise is unnerving and a nuisance at worst but it is not a problem. It will dissappear after some hours of use. I had the same noise on my F225 engines. So far after 725 hours, the still run like a swiss clock. Here's a picture of the area in question taken of my engine. If you look just beyond the head of the bolt, you will see the drive shaft. The only belt is the timing belt and that's a cogged belt that won't normally slip. Hope this helps and calms any panic and fears.
