Find a way underground to search for the source of the Fallen jamming signal.
- Make your way over to the next marked location, just past the Public Event Plaza, down by the river shore.
- This is the entrance to the Lost Sector: Scavenger's Den. Go on inside.
- Head down the tunnel and through the far door on the right-hand side.
- Look to the left as you pass an entrance to possibly find a chest.
- Go through the door in the back right and drop down over the few ledges into the water below.
- Go forward, following the underground river.
- Climb onto the lower ledge in the back of the cave.