I remember as a kid that I used to like to figure out how things were designed and put together. After completing Doom, I remember experimenting with noclip. I don't recall if it worked in all of the maps, but I specifically remember that on one map in particular, you start inside with a bunch of explosive barrels. Eventually you work your way outside and the "end" of the level is you reaching a large teleporter platform. This I believe was the "ending" of a chapter or such because a text popup occurs after. On that particular map, I NOCLIP-ed out of the map and decided to just run away as far as I could away from the actual map area. As I traveled through the "noclip" land (where the graphics are all glitchy since you're not actually "in" the legitimate map area), I started to hear howling from "alerted" enemies (such as when the enemies know you're around and are looking for you). As I continued to go farther away from the map, the howlings became louder and louder, as if I was actually approaching a horde of enemies. It probably sounded like at least 30+ enemies. Eventually I got so close that suddenly I was "there", wherever "there" was. The howling turned into a crazy spamfest of scratching noises (like being melee'ed) and such noises of being attacked. It sounded like I was in a room full of enemies and they were all attacking at once. However, you still couldn't see a thing as you weren't actually in any part of the actual map.

Does anyone know what this was? Did the map designers hide all of the enemies in the map all in one "out of bounds" area of the map before they are teleported in or something?