Is my alternator about to kick the bucket?

I had my water pump replaced at the end of last season, and had the boat in the water on Sunday this week. Everything ran fine, and my alternator is producing a charge and all, but it's making some "clunking" sounds at idle. Was thinking the a bearing in the alt is going out on it?

Can I replace it with a stock automotive alternator? It's an Indmar Monsoon 310hp (Chevy 350).

Thanks