Payday - The Witch

Brief Overview
The PAYDAY series is a co-op first person shooter made by Overkill Software, the game itself is not a horror by any means, but the developers have put in a few hidden screamer easter eggs in their games.

No Mercy - The Witch
In July 2012 a new heist was added to the game which takes place in the No Mercy hospital from the Left 4 Dead series, halfway through the heist the power might get cut, during this time, there's a small chance that the player may hear the iconic crying of the Witch from Left 4 Dead, the player can see her crying in a locked, inaccessible room.

Once the player looks at her, she suddenly appears at the door, face pressed against it and screams at the player, before quickly disappearing. Whoever the player is playing as, they will respond in shock.

Unknown if this still occurs in Payday 2.

Lab Rats - The Giant Spider
As part of the Halloween update in October 2015, a new heist was added called Lab Rats in which the group are shrunk down to the size of ants and the entire heist takes place on a table.

Occassionally, a giant spider makes an appearence on the map, not doing much, though a jumpscare can occur with this massive spider.

If the player stares over the edge of the table on the right hand side, the spider may suddenly jump up without a warning and down the players nearby.

LINKS
WARNING: The following videos contain a screamer AND a massive spider!

PAYDAY The Heist: - The Witch www.youtube.com/watch?v=qLBr3vU-6UE

PAYDAY 2 - Spider - www.youtube.com/watch?v=zagPfuYVKNw (NOTICE: This video shows another player being jumpscared/attacked by the spider, from the view of another player who's at the other end of the map, still contains spiders.)