So at lunch today, I was able to kill 3 of these. I got some cool loot, plans and scrap. They do make a VERY distinctive noise. It starts out as like radio static noise - like a constant staticy noise. As you get closer it sounds like Morse code with beeps and gets louder the close you get. They are easy to see as they have huge junky looking backpacks on. You do not have to look in ever building or nook and cranny. Interestingly they run from you more often than fight. I saw two one star and 1 two star. Two were in Welch and 1 at Mt. Blair. The one in Mt. Blair was two levels above me and I heard it from the ground. And I did the event on the FO 1st server as well.
Just passing along the info.