Abnormal "Halifax hum"

An investigation into the cause of a mystery humming sound
(https://bbc.in/3Jkbtou) which has plagued villagers for more than
a year has identified three possible sources.
Residents in Holmfield, near Halifax, said the noise had "tortured"
them in their homes and damaged their health.
The low-level hum was first reported to Calderdale Council in
September 2020.
The authority has not revealed the possible causes but said a
"significant amount of effort and resources" had been devoted to
resolving the issue.
Villagers have previously said they thought local industrial units
were to blame for the drone, but an initial council investigation
identified "lots of potential sources".
Updating residents at a recent council meeting councillor Jenny
Lynn said the inquiry had since narrowed down the list of probable
causes.
She said: "I can tell you at this stage we believe there are three
possible sources of noise nuisance in the process of being
investigated," according to the Local Democracy Reporting
Service.
She said that despite being unable to publicly reveal the sources
residents should be reassured "a significant amount of effort and
resources" are being put into finding out the cause.
"Investigations into low-frequency noise complaints are complex
because the alleged noise can't usually be heard by most people
except the complainant and perhaps a few other individuals,"
she said. "The work is ongoing and officers are in touch with
everyone who has expressed concern."