Distress signal (Relay tower 1DL-109)

Distress Signal is a quest in Fallout 4.

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

Detailed walkthrough
Go SE from the radio beacon until meeting the train tracks and find a train with several feral ghouls.

The fourth car along (blue car, turned on its side) has a hatch to enter the train, hidden behind a bush. If having difficulty finding it, it's the only bush touching the train on either side.

Inside next to a ham radio are the skeletal remains of another body along with the radio signal and a locked crate.

Bugs
This signal and the nearby Boston City Works Beacon and Garbled Radio Beacon do not turn off when their original ham radios are turned off by the player.