might be the looney with the rigged alley? there is a wastelander on the other end saying that he has been yelling for days. the alley itself is rigged with several mines, mini nukes etc. once he sees you down there, he will blow the whole alley sky-high. possible to gather some of the explosives, maybe all of them with a sneak boy. easiest way is to snipe him in the head, one-shot kill preferably.
He is normally called The Preacher for more info http://fallout.wikia.com/wiki/The_Preacher