Distress signal (Relay tower 1DL-109)

Distress Signal is a quest in Fallout 4.

Quick walkthrough
Found when extending the Relay Tower 1DL-109. Woman says she is hiding in train car with "Thomas." Shortly into recording she describes her hiding spot as a train car.

Detailed walkthrough
Follow the rail line south to find a train with several feral ghouls. Crouch near the overturned blue train near bushes by a cluster of trees to enter it. The door is hidden by the bushes, and is a small hatch. Inside next to a ham radio are the skeletal remains of the woman in recording, along with a locked crate.