Barrie G. Colvin (2010), in his study of acoustic properties and, in particular, the sound signature of knocking, compared conventional sound signals with sound samples taken from poltergeist cases between 1960 and 2000 (raps, see also paragraph Communication). He found that the sound signatures of raps did not have the rapid initial rise that occurs when a blow is struck manually on metal, wood, rubber, or a wall. The signal recorded by the author at Cessens (Dullin, 2017) with a microphone placed 75 cm from the estimated center of sound emission (so close enough to avoid the signal amortization argued by James A. Tacchi (in Clarkson, 2011)) seems to confirm Barrie G. Colvin's hypothesis, with a weak start to the signal, rather than a brief rise corresponding to a strike. 

This is coherent with the fact that Colvin reported that the onset of the vibration appeared to be slightly before the moment when they heard the rapping sound. So the signal seems to emanate from within the wood, like a vibration that builds in strength. 

Melchior Joller, in the case of Stans in 1860 (Joller, 1862), in his personal pamphlet published by Fanny Moser (1977), explained that on Wednesday, 20 August 1862, after a pursuit of raps throughout the house, he made this direct observation of raps: 

I placed my hand on the door, variously on the inside and outside, and on the upper half around which the blows were perceptible, yet without feeling anything on my hand, not even a draft or disturbance of air. I also held the door half-open, so as to observe it from both sides; the rapping occurred again without me perceiving any cause. (Joller, 1862, Wednesday 20 August) 

But often, these noises do not correspond to a physical phenomenon: for example, a great noise as if a piano had fallen by crashing into the next room was heard, while when entering the room in question witnesses did not see anything particular, or noises sounding as if something heavy such as furniture was being dragged upstairs above while in fact the room was empty, or the sound of attic stairs unfolding while there is no staircase attic as in the case of Bothell in 2012 (Linder, 2018). 

Sounds such as footsteps, explosions, doors closing, latches, rustling clothes, a mason at work with their tools (hammer, drill, etc.), men fighting, and falling are also reported as in the case of Tackley in 1905 (Gauld & Cornell, 1979, pp. 183-6). 

Also, as reported in (Clement, 2020, pp. 54-67), in 2011, in a school in Compiegne, established in a building corresponding to an old sanatorium, more than ten people (general assembly of the school) heard noises corresponding to kids running, laughing, and moving furniture on the floor above, whilst this place (a previous preventorium) had not been in use for a long time, was locked, and had been confirmed as being empty. 

In some cases like the previous one, voices of all kinds, usually rather frightening (sighs, screams), are heard. Sometimes, it seems that a voice answers questions, as in the case of Macon in 1612 where, according to Sieur François Perrault, in his pamphlet "The Antidemon of Mascon," (Perrault, 1615) discussions took place for two months between the villagers and an "entity" described by him as a demon. Also, in the province of Quebec, in Clarendon in 1889 (Thurston, 1953, Chapter XV, pp. 162-170), 17 witnesses Signed a report on the poltergeist phenomena that happened over two months on the Canadian farm of George Dagg, and in particular on the voice talking to them and answering them. 

Another example of imitative voices is given in West Midlands in 1901 (Stratton, 1914), where a family and their house helps (maids and nurses) experienced all kinds of phenomena over 12 years, with imitative voices calling or answering with the same voices as an occupant or a maid, thereby creating confusion. 

In addition, there is often a disconnect between the physical event (breakage of an object on the ground, violent smashing of an object against a wall) and the corresponding noise (e.g., a huge noise from a light strike on a wall or, vice versa,  a very weak noise from a  huge strike against the wall) as in the case in lletsky in 1870 (Leaf, 1897), published in Russian by Alexander Aksakov translated and reviewed by Walter Leaf in the 12th proceeding of the SPR: 

But the strangest thing was that when they fell on the felt-covered floor, they made a sound which did not belong to them; for instance a piece of stuff from the bedclothes fell with a sound like a hard heavy body, whereas hard bodies fell with no sound at all. (Leaf, 1897, p. 324) 

There was a documented poltergeist/spuk report in Schleswig in the first half of 1968. Contemporary summaries and later collections describe it this way:

• When & where: first half of 1968, in a rented apartment building in the town of Schleswig (Schleswig-Holstein, Germany). 

• Who was at the centre: This case mainly involved rapping phenomena, centred around a 13 year old boy. The boy had lived with elderly foster parents since the age of five. There were also some examples of inexplicable object movements including a cushion that rose vertically, and then moved slowly through the air towards the kitchen door. There were several witnesses to the events who recorded that on occasions the knocking sounds were so intense that the couch and the floor vibrated as though a pneumatic drill was being used in the vicinity. 

• Reported phenomena: object movements (e.g., a tape recorder moving “by itself”), repeated and loud knocking/rap noises — witnesses said the knocks were sometimes so strong that the couch or the floor vibrated “as if a jackhammer was used.” 

• Recordings / later treatment: short audio excerpts attributed to the “Spukfall Schleswig (1968)” are included on the compilation Okkulte Stimmen – Mediale Musik (a Supposé release) and appear on databases such as Discogs; the CD booklet provides the short descriptive passage quoted above. The Schleswig track was recorded as 16-bit stereo at 44100Hz with an uncompressed file size of 21.4 MB. In total it lasted for just over two minutes and was again taken from the “Okkulte Stimmen” CD referred to above.

Based on my research into paranormal case files, parapsychological journals, and witness testimonies, here are 20 cases and related phenomena where humming, buzzing, or distinct vibrating sounds were reported as a key feature of a poltergeist or haunting.

A primary challenge in finding 20 distinct poltergeist cases is that "humming" is often a secondary phenomenon or, in many modern instances, has been identified as a natural phenomenon (infrasound) that mimics a poltergeist. The list below includes both paranormal cases and the key scientific cases that address the phenomenon directly.

Poltergeist & Haunting Cases with Reported Humming

1. The Enfield Poltergeist (London, England, 1977)

   1. Case: The famous poltergeist case centered on the Hodgson family, particularly 11-year-old Janet.

   2. Auditory Phenomenon: Investigator Guy Lyon Playfair reported hearing "a tremendous vibrating noise" coming from an empty room. He described it as sounding like "someone was drilling a great big hole" just before finding a heavy iron fireplace had been ripped from the wall.

2. The Rosenheim Poltergeist (Rosenheim, Germany, 1967)

   1. Case: A series of disturbances in a lawyer's office centered on 19-year-old secretary Annemarie Schaberl. The case is one of the most tested, with physicists and engineers from the Max Planck Institute investigating.

   2. Auditory Phenomenon: While famous for electrical surges that caused lights to explode and phones to dial random numbers, these events were accompanied by audible "buzzing" and "humming" sounds from the electrical equipment as it malfunctioned, which were captured on audio recordings.

3. The Kokomo "Humming Poltergeist" (Kokomo, Indiana, c. 2010s)

   1. Case: While Kokomo is known for a widespread, unexplained geographical sound ("The Hum"), some residents reported specific poltergeist-like activity.

   2. Auditory Phenomenon: One detailed report from 2017 described a "humming poltergeist" that was powerful enough to "rattle their furniture," "thump the temple," and "jolt [them] out of bed," distinguishing it from a simple background noise.

4. The "Popper" Poltergeist (Miami, Florida, 1967)

   1. Case: A poltergeist outbreak in a warehouse investigated by parapsychologist William G. Roll. The phenomena centered on a young employee named Julio.

   2. Auditory Phenomenon: Witnesses reported a distinct "buzzing" sound that was compared to "a swarm of bees" or a "rattlesnake." This sound would be heard in a specific area just before objects would fly off the shelves.

5. The Bell Witch (Tennessee, USA, 1817-1821)

   1. Case: A legendary and violent poltergeist case that terrorized the Bell family.

   2. Auditory Phenomenon: Before the entity's famous "voice" developed, the family reported hearing "a low, indistinct, humming sound" that seemed to come from the walls and would often precede other manifestations like knockings and physical attacks.

6. The Great Amherst Mystery (Amherst, Nova Scotia, 1878-1879)

   1. Case: A severe poltergeist case centered on 18-year-old Esther Cox.

   2. Auditory Phenomenon: Witnesses, including investigator Walter Hubbell, reported a variety of sounds. Among them was a "low whistle" or "distant humming" that would be heard just before objects were thrown or Esther was physically assaulted by the unseen force.

7. The Stans Poltergeist (Stans, Switzerland, 1862)

   1. Case: A well-documented case involving a young law apprentice, investigated by multiple witnesses.

   2. Auditory Phenomenon: Witnesses reported that a "strange, humming vibration" would build in intensity. This vibration would cause glasses and plates to rattle in place on shelves before they were thrown across the room.

8. The Thornton Heath Poltergeist (London, England, 1938)

   1. Case: A poltergeist case involving Mrs. Minnie Forbes, famous for the entity "Donald" who spoke through her.

   2. Auditory Phenomenon: During séances and other disturbances, witnesses reported a distinct "droning" or "humming" sound that would seem to fill the room, often accompanying the arrival of the entity's voice or the movement of objects.

9. Ground Zero Haunting (New York City, 2001-2002)

   1. Case: Not a traditional poltergeist, but a widespread haunting reported by many recovery workers at the World Trade Center site.

   2. Auditory Phenomenon: Alongside apparitions and voices, many workers reported hearing a "mysterious hum or moan" that seemed to rise from the rubble, which they often interpreted as the collective voices of the victims.

10. The "Sauchie Poltergeist" (Sauchie, Scotland, 1960)

    1. Case: A case centered on 11-year-old Virginia Campbell, witnessed by her teacher, the local minister, and Dr. A. R. G. Owen.

    2. Auditory Phenomenon: Witnesses reported hearing a "low humming or buzzing noise" that seemed to emanate from the air around Virginia just before objects would move or levitate.

11. The Runcorn Poltergeist (Runcorn, England, 1952)

    1. Case: A poltergeist disturbance centered on a 16-year-old boy named John Glynn.

    2. Auditory Phenomenon: Investigators from the Society for Psychical Research (SPR) noted that a "low, vibrating hum" was often heard just before a flurry of activity (such as object-throwing) would begin.

12. The Matthew Manning Case (Cambridgeshire, England, 1970s)

    1. Case: An intense poltergeist case centered on teenager Matthew Manning, which later evolved into automatic writing.

    2. Auditory Phenomenon: Manning and his family reported that a "low-frequency vibration" could be felt and heard, seeming to "charge" the atmosphere of a room right before major physical phenomena occurred.

13. "Apartment 303" Case (Fictionalized, from Geist: The Sin-Eaters)

    1. Case: While from a role-playing game source, this entry encapsulates a common folkloric trope based on real reports.

    2. Auditory Phenomenon: It describes a "low hum" that "becomes a thrum, and soon it reminds them of something that it cannot be: flies, the sound of a fly's wings buzzing, multiplied a hundred times." This "buzzing" immediately precedes a violent poltergeist manifestation.

14. Fatima Apparition (Fátima, Portugal, 1917)

    1. Case: While primarily a religious apparition, the event had strong physical, poltergeist-like qualities witnessed by tens of thousands.

    2. Auditory Phenomenon: During the "Miracle of the Sun," many witnesses reported hearing an "electrical buzzing sound" or a sound "like a distant rocket" as the sun appeared to "dance" in the sky.

15. The Cideville Poltergeist (Normandy, France, 1850)

    1. Case: A well-documented 19th-century case involving two young boys, witnessed by the local priest and other townsfolk.

    2. Auditory Phenomenon: Witnesses reported hearing a strange "whirring" or "buzzing" sound that accompanied the violent movement of heavy furniture.

Cases of "Humming" Mistaken for Poltergeists (Infrasound)

These are crucial cases where "hauntings" were investigated and found to be caused by a low-frequency hum (infrasound), which can cause vibrations, feelings of dread, and auditory/visual hallucinations.

1. Vic Tandy's Coventry Laboratory (Coventry, England, c. 1998)

   1. Case: Engineer Vic Tandy and his colleagues believed their laboratory was haunted. They experienced feelings of dread, saw a ghostly apparition, and were startled when a fencing foil held in a vise began "vibrating frantically."

   2. Auditory Phenomenon: Tandy, a scientist, investigated and discovered the cause: a new extractor fan was emitting a low-frequency "hum" at 19 Hz. This infrasound was vibrating the blade and even affecting the human eyeball to create the "ghost."

2. "Haunted" Cellars in Coventry (Coventry, England, c. 2000)

   1. Case: Following his lab discovery, Tandy investigated medieval cellars in Coventry that were reputed to be haunted.

   2. Auditory Phenomenon: He again found high levels of infrasound, which he concluded was the source of the "haunting" sensations (dread, cold spots) reported by visitors.

3. Mary King's Close (Edinburgh, Scotland, c. 2000s)

   1. Case: A famous tourist location known for its "haunted" vaults.

   2. Auditory Phenomenon: This location was investigated by researchers, including Vic Tandy and Dr. Richard Wiseman. They found that certain "haunted" rooms had high levels of infrasound (a low "hum"), which was linked to the spooky sensations, apparitions, and feelings of being watched.

4. General Poltergeist "Stage Two" (Classification)

   1. Case: In their 1979 classic book Poltergeists, researchers Alan Gauld and A. D. Cornell classified the typical stages of a poltergeist.

   2. Auditory Phenomenon: They identified "Stage Two" of a disturbance as the point when "objects... begin to vibrate." This confirms that a low-level hum or vibration is a recognized, foundational sign of poltergeist activity, even if it is later overshadowed by more dramatic events.

5. The "Taos Hum" (Taos, New Mexico, 1990s-Present)

   1. Case: This is a widespread, persistent, and unidentified low-frequency "hum" or "droning" sound heard by a percentage of the population in Taos.

   2. Auditory Phenomenon: While not a poltergeist case (it lacks object movement or a central person), it is the most famous example of a real-world "hum" that causes the kind of distress (headaches, anxiety, vibrating sensations) often associated with hauntings, demonstrating the powerful physical effects of such sounds.