Electronic voice phenomena are electronically captured sounds that resemble speech, but are not the result of intentional voice recordings. Common sources include static, stray radio transmissions and background noise. Some people claim these sounds are of paranormal origin. Others claim there are natural explanations such as apophenia (finding significance in insignificant phenomena), auditory pareidolia (interpreting random sounds as voices in their own language), equipment artefacts, and simple hoaxes. Recordings of electronic voice phenomena are often created from background sound by increasing the gain (i.e. sensitivity) of the recording equipment.
The term electronic voice phenomena (or phenomenon in the singular) is commonly abbreviated as EVP. (Wikipedia)