[jlex]

And don't ever ever ever continue to drive the car if you hear something like that again or if the alternator light goes on. Being air cooled, the engine may get ruined the next time if you continue to drive it. Be very aware of weird engine noises. Stop the engine and check it out immediately. You don't need to remove the alternator belt to replace the AC belt and can run the car just fine until you get a replacement belt, but unless I knew the history of that alternator belt, I'd replace it at the same time just for the peace of mind.
Think about getting a Bentley repair manual. That and this forum will help you keep the car on the road.