Signal Yankee Bravo

Signal Yankee Bravo is a radio transmission just south of Canterbury Commons, southwest of Robot Repair Center, and north of Corvega factory, which is activated by a switch on a transformer there. Although identified as "Signal Yankee Bravo", it actually broadcasts the sound of labored, heavy breathing.

Just west-southwest of the tower, at the base of the drop-off, is a sewer grate to a drainage chamber. On entering, the door to the right leads to feral ghouls (and possibly a glowing one at higher levels) hovering around a ham radio, making them responsible for the broadcast. The ghoul sounds can still be heard in the signal even after the ghouls are killed, even if you turn the radio off ("click"), then back on. (You have to select the station on your Pip-Boy again.)

There is also a large hole in the wall to the left from the entrance that leads to a small cavern with several feral ghouls and a glowing one (also depending on your current level). There is nothing of note in this room except a very strongly radioactive junk pile in the far corner.

Notable loot
A copy of Grognak the Barbarian, on the same metal shelf underneath the ham radio, the signal of the yankee bravo radio broadcast