Ghoul Problem

Ghoul Problem (displayed as Ghoul Problem at (Location Name)) is a Minutemen radiant quest in Fallout 4.

Detailed walkthrough
After joining the Minutemen, this quest can be periodically obtained when talking to Preston Garvey or listening to Radio Freedom. The Sole Survivor is informed that an allied settlement is having trouble with some feral ghouls, and is asked to help the settlement deal with them. Alternatively, the quest may be obtained directly from a settler even if the Sole Survivor has not joined the Minutemen (this occurs more frequently at unowned settlements).

To proceed with the quest the Sole Survivor must travel to the settlement and talk to their leader, who will give the details: a large group of feral ghouls has settled in nearby. The settler will point the Sole Survivor to the ghouls' hideout and ask that they be eliminated for the safety of the settlement.

To complete the objective, the Sole Survivor must travel to the ghoul hideout and eliminate the marked feral ghoul. Unmarked enemies do not need to be killed to complete the quest. With the threat neutralized, the Sole Survivor can talk to the settler from before to receive thanks and a reward of ~100 caps, as well as ownership of the settlement (if it was not already owned). If the quest was given by Preston Garvey, the Sole Survivor must report back to him to turn in the quest; it will be completed immediately upon receiving the reward otherwise.

Bugs

 * If the player character is sent to kill the feral ghouls at Fiddler's Green, Super Duper Mart, Mass Pike Tunnel, or generally any place given even they have already been cleared before and after receiving the quest, a quest marker may not appear and the quest may get stuck. Killing all the feral ghouls in that location may not update the quest. If this occurs, allowing time to pass until the quest fails may be the only way to complete it without console commands.
 * The only non-cheating method of completing the quest if waiting doesn't work would be to outright murder the current settlers and forcefully take over the settlement workshop. This can also be accomplished by doing Home Sweet Home or Claiming the Commonwealth
 * Alternatively, the console command can be used to proceed to the next step of the quest and report its success to the settler.
 * Sometimes the targeted ghoul may become stuck somewhere that the player character can't reach. The only way to kill the ghoul is by using explosives or other area-of-effect weapons.
 * In certain locations, NPCs might spawn in inaccessible locations (for instance, Roger Warwick at Warwick homestead might spawn inside the water cistern). This bug is shared with the other settlement quests.
 * This can be resolved by using the console command to teleport the NPC in question.
 * The Warwick homestead example can be resolved by building stairs into the cistern and a bell outside of it. Using the bell and waiting for an in-game hour (using the Wait option) will cause the NPCs to spawn near the bell.