Man, those spider-things are creepy! Like, far more creepy than anything else in the game! Yikes!
But what adds MORE creepiness is the fact that they seem to keep generating these odd, scary noises even when defeated. Not cool, spiders, not cool! I kept looking for more of your kind, only to find that nope - it were the bodies all along. That, or they had a friend stuck in geometry somewhere nearby - but I don't think that was the case... when I came back later to the same spot, with the bodies now de-spawned the noise was gone.
Also, they don't drop anything useful, the little bastards! (This last bit probably isn't a bug, but SHOULD BE, given how creepy the spiders are!)