Knocking sounds

[Gabry_Polo]

So, i was playing people playground, killing people and stuff, untill... i heard some rumbling, like if someone was crawling in a vent. I didnt taught of it, imagining it was just some creepy sounds, but then i heard knocking on metal, and something heavy falling, i quitted the game in seconds, and i try to recreate what i was doing but nothing makes the sound play again, anyone know what is this sound about? Or if anyone ever experienced it?

[duh outlaw]

people playground fans when ambient sounds

[joe.alton1]

it's just a sound that sometimes plays.