Residents within earshot of HMRC's huge regional HQ in Bristol say they are being "driven mad" by alarms ringing out from the building.
The eight-storey office opened near Temple Meads last year, at Glass Wharf, and 1,650 HM Revenue and Customs (HMRC) staff will eventually be based there.
This week neighbours have complained of "torturous" noise blaring from the riverside building, and HMRC has now apologised and explained what the racket was.
Tweeting last night (July 22), Catherine Downer told HMRC: "Local Bristol residents are plagued night after night by the incessant alarms at your new building on Glass Wharf.
"Please, please, this has to stop. It’s unbearable!"
In a further complaint directed at Bristol City Council, she added: "South Bristol/Totterdown residents are being driven mad night after night by the HMRC alarms that sound every minute of every evening at the moment.
"The noise emanates from 3 Glass Wharf."
Steve Mathews responded: "It's been happening since long before lockdown and is actually torturous."
HMRC has apologised to its neighbours and explained that the noise was the result of fire alarm tests.
It has said it will work with contractors in future, to ensure any future works are carried out during the daytime where possible.
A spokesperson told Bristol Live: "The fire alarm system at our Glass Wharf office at Temple Quay was tested each evening between Monday July 13 and Thursday July 16, and on Monday July 20 (yesterday).
"We moved into the building last year, and these tests were carried out after the recent installation of a new building evacuation system.
"The fire alarm and evacuation system testing work has been completed, and we apologise for any inconvenience caused to local residents."
As required of all employers, there is a fire alarm test each week, which might be what Mr Mathews was referring to pre-lockdown.
Bristol residents are no stranger to odd noises - from the mysterious Bristol hum to the Severnside Sirens at Avonmouth.
The latter warns people of possible incidents involving dangerous substances, with residents instructed to stay indoors and close windows and doors if they hear the siren sound.
It is tested on the third day of each month at 3pm.
