Floors and ceilings moving silently

Large door sectors (as well as lifts, crushers and other moving floors) opening silently or quietly is a bug that occurs due to the way Doom handles sector-generated sounds.

The Doom engine places the origin of the sound when a sector makes a noise (door, crusher or lift) at the center of that sector. When a sector spans a large area, the distance between the player and the point of origin of the sound can be sufficient for the player to hear no sound, despite being right next to the sector.

The oddity is audible (or not so) in Memento Mori II MAP07 which uses such a method for a door that "jams" at random positions, and also a few maps of 10 Sector that use large sectors to cover multiple doors that open at the same time. When the sound code was changed in ZDoom to place the point of origin of the sound at the nearest point of the sector from the player, the change broke some maps which deliberately used this effect, notably Suspended in Dusk. As a result, a compatibility flag and map option was added shortly afterwards to optionally restore the old behavior.