[Putershark]

In theory,
Really not much difference between the 2 engines (just materials and configurations) between a 4 stroke Outboard and a Automotive engine. First thing I would check would be the alternator belt adjustment and or alternator shaft bearing making noise. Then either adjust the alternator belt, or have the alternator replaced (if still under warranty) to help kill the shaft bearing noise

If not under warranty and the belt adjustment does not correct, I have seen alternators last a very long time with a little squeak from the shaft bearing before they fail and unless real loud, I would not worry much about it as long as the belt is adjusted corrected and not getting real hot and or slipping from the bearing locking up