Dungeons & Dragons is deprived of much of its atmosphere of
mystery and frightfulness when it loses its element of surprise. Experienced
player/DMs know all the monsters, and nothing <link>
comes as a surprise to them, excluding the inventiveness of the presiding
DM.

Moreover, what's a good dungeon without thick cobwebs and odd
stains, not to mention the screams wafted randomly on the wind? What
does silence mean if there is no noise to contrast it? Non-surprising
monsters could make themselves known by noises, ie, drum beats,
cheers, curses, shouts, and the tramp of many feet could announce the
arrival of a band of Orcs. Furthermore, some noises could be heard
that have no bearing on play. Try these tables on some unsuspecting
players and watch them get very cautious!

Every 30 minutes, there is a 25% chance of hearing a random
noise. Such noises will either cease if investigated, or lead investigators
away, possibly to a trap. These noises will seldom lead into a position
where their prospective cause could be seen.
 

Die Roll	Result
1	Moans or groans
2	Screams or shrieks
3	Rattle of armor
4	Insane laughter
5	Footsteps
6	Sounds of battle
7	Scratching or scraping
8	Mumbling
9	Sobbing
10	Wind
11	Creaking
12	Drums
13	Whispers in an unknown language
14	Muffled explosions
15	Thuds
16	Roars
17	Rumbling
18	Slamming doors
19	Squelching or other sounds of non-human passage
20	Heavy breathing
21	Rattling dice/ DM’s screams of anguish/garbage disposals/ etc.

These sounds are also good for “noise rooms”. Note that these
noises could be distorted, or sound more distant due to the acoustical
qualities of dungeons.

For the same chance, a few visual goodies are also frustrating.
Note that these apparitions are real to all senses, including touch, but
they vanish immediately after the party has left.
 

Die roll	Result
1	Blasted or melted stone
2	Cracks in walls, floor or ceiling
3	Moss
4	Dark mist
5	Light mist
6	Thick cobwebs
7	Bloodstains or pools
8	Damp patches
9	Bulging walls
10	Luminescent areas
11	Shadows that are wrong (ie: An iron spike having the shadow of an Ogre)
12	Footprints, or a trail
13	Pitted or corroded spots
14	Trail of blood
15	Rusted, useless armor or weapons*
16	Exceptionally thick dust
17	Slime (Not Green Slime!)
18	Scorched sections
19	Chipped spots
20	Corpses shackled to the wall

*If these are picked up, or touched, they will immediately flake away to
piles of rust.

These apparitions are great for misleading players, ie; when they
use them as landmarks, and return to find them gone.