Spirit tapping is a phenomenon said to be heard during seance

Séance

A séance is an attempt to communicate with spirits. The word "séance" comes from the French word for "seat," "session" or "sitting," from the Old French "seoir," "to sit." In French, the word's meaning is quite general: one may, for example, speak of "une séance de cinéma"...

 and spirit invocations as evidence that a spirit is making contact with the medium and seekers. It was a chief type of purported spirit demonstration in the early 19th century.

Many claimed that it was a spiritual Morse code

Morse code

Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

 and other various claims or origination. Eye and earwitness accounts of such activities have been reported, as has the discovery that many times the sounds were being made under the table by or in the pockets of various magicians

Magic (illusion)

Magic is a performing art that entertains audiences by staging tricks or creating illusions of seemingly impossible or supernatural feats using natural means...

, charlatans and spirit mediums themselves.