I know that radiant quests are supposed to continue forever, but something is causing them to be given constantly at Sanctuary. I can't even go there any more because every time I turn in a quest, Preston gives me another. It never stops. If it's not ghouls or raiders, it's constant kidnapping from probably the best-fortified place in the Commonwealth. Please, dial down the frequency!

According to the dialogue, these settlements should now join the minutemen - which is great, except they joined ages ago. Finch Farm has apparently decided to join us at least seven times so far. It's infuriating.

This isn't a bug. Each time you go to Preston you pick up a new quest. This is how radiant quests work. Don't go to him, and you won't pickup any more.