https://www.pcgamer.com/battlefield-1-easter-egg-teases-a-new-battlefield-reveal-later-this-month/

EA's Battlefield games are well-known for their Easter eggs, some relatively simple and others ridiculously complex. Unraveling their mysteries has become something of a cottage industry among Battlefield fans (there's an active Discord, if you're interested in that sort of thing), who recently discovered the secret behind a Battlefield 1 door that's remained locked for a year. 

Found in the Fort de Vaux map of the They Shall Not Pass expansion, the door is labeled "Isolement"—French for "Isolation." But what makes it noteworthy are the sounds coming from behind it, which you can hear in the video below. Creepy stuff.