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 generates an invisible object in the center of a sector when a door, crusher or elevator is used. The appropriate sound is then played from this object and of course, the further away the player is from it, the fainter the sound. When a sector spans a large area, the invisible sound object could be generated a fair distance away from the activating line. If the object is far enough away from the activating line due to a sector covering a large area, the sound may only be heard faintly or not at all.

This has likely been around since the Vanilla days and still occurs in modern source ports such as ZDoom.

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.