Platform: PC
Description: I lured Hunters and Ticks away from their location and killed them, then came to that location and their sounds were still there. I think.
Steps To Reproduce: Kill a bunch of Machines, leave the area then come back.
Images / Videos:
Host or Client: Solo Session
Players in your game: Just me
Specifications: Win10, 16GB RAM, Geforce 1070, Intel Core i3-8350 4.00Ghz
It also happens when you kill a robot clipping through a wall, it makes weird noises. And it looks like it’s trying to get unclipped.
At first I thought the enemies were stuck beneath the ground, but there was no threat indicator. So we go from dead enemies making undead noises, to ghost enemies. A bit creepy almost 
It happened to me too wth a bunch of hunters, runners and drones
I had something similar 2 days ago.
Me and my friend went on a killing frenzy on an airfield. There some of the runners were making hunter/tank/seeker sounds right after killing them 
I had the same several times.
The sounds from beyond was something that turned up in the April Update and was supposed to have been rectified in the May update.
this doesnt seem to happen as much now , but i have noticed in a coop game, if they kill bots when i am not present and i return ( say if i get killed and have to respawn and run back ) , i will hear them when they are dead.
I’ve seen this occur mostly when I kill a dog and it’s stuck on part of the environment. For example, if it’s killed next to a door in a bunker, and you open/close the door on it, it will make clanky metal sounds from the dog’s body continuously until I run away or log and the dog despawns.
I’ve also heard weird sounds when the machines are clipping through walls. Such as when they come through a barn wall, or hunters fall through the ground to a bunker underneath them (boy did that scare me good the first time it happened…)
Seems same to me. In Vesslan bunker I killed two green runners in the room with some silos and a large iron gate. One of them stayed in a form of on an invisible fantom, playing some sound and blinking. Tried to shoot at it, without effect. The second runner resulted in a usual corpse and could be looted. Platform PC.
The bit that annoys me is where you start searching because you hear a seeker, only to find it was one you destroyed ages before but still making it’s flying noises
Very true. Happens all the time for me. 
Still having this happening on the PC version as-of the June update, with the additional issue that sometimes it’s happening in places there weren’t even machines to begin with.
I have noticed that the bug has uhm, evolved. It’s rare, but now, enemies can actually be stuck underneath the ground. I’ve encountered areas where there’s supposed to be machines, and yet there’s nothing. I can hear them, and sort of pinpoint where they are, and if I use an explosive weapon the splash damage will hurt them. I’ll see if I can record this next time I see it.
Had that happen yesterday at Saltholmen Naval Base. A seeker got stuck under the ground near the eastern checkpoint.
Still happening. Occurred last night. Defeated enemies and “ghost” enemies making noises. My best guess is they were trapped in the terrain somewhere.
I was thinking that. But the ghost seeker sound definitely comes from above me all the time.
if i could add , i would think perhaps it could do with the time that machines are still around in the world after they die ( despawn time if you like ) , and also if they glitch whilst invisible / dead / inactive.
Usually these ghost sounds stay forever (until game restart).
I have had these ghost sounds from the day i bought the game.
But now recently after killing robots, 2 sounds are most like to appear. Seeker buzzing to dead tank location. (some times beep like detecting player and ping sounds)
Other is dead Hunter turns into ghost Tank making sounds.