I kept getting that same quest too. I did it three times before just ignoring it.
Now I have a "kidnapping in Sanctuary Hills" quest to complete. The quest? Raiders kidnapped a settler. They're holding him at the Federal Ration Stockpile. It's literally the exact same mission but in a different settlement. This is really getting old.
A lot of people have offered tips on how to stall all of the freakin Minutemen quests. Getting them to the point where it just says 'Talk to Preston' will prevent new ones from coming up. I'm currently working on maxing out Preston's affinity for me so I can get the perk. Once that's done and I've unlocked all of the settlement locations, I'm done with him until the main quest coincides with him again. I'm traveling with him right now for the first time since starting the game. He's the most utterly worthless companion so far. I've traveled with Dogmeat quite a bit, and I've traveled Piper, Cait, and Curie enough to max out their affinity. They all have their own flaws, but Preston is worthless. Half the time I can't even find him because he's running off somewhere.