A MYSTERY noise is causing sleepless nights for residents living on the city's waterfront.

The residents around Buchanan's Wharf, off Redcliffe Street, are regularly disturbed by a piercing alarm, which goes off intermittently in the early hours of the morning, but have yet to identify the source.

Suggestions about the mystery sound ranged from devices to keep seagulls off the buildings and faulty office alarms activated by the weather.

One resident, who wanted to remain anonymous, said he had been woken up several times in the night over the last three weeks.

It is thought that only flats facing the water are affected by the alarm, which sounds at about 4am, coming from the Welsh Back area.

Auriol Ashley, 71, retired, has lived in the north block with her husband since 2001. She has been bothered by it in the past.

She said: "This alarm has been going off for years – I think it is the wind which sets it off. I have called the council's noise pollution people about it.

"It is a continuous alarm in the early hours of the morning which wakes you up, then it goes off and comes back on again. It doesn't happen every night but happens every now and then. I believe it is one of the office blocks on Welsh Back.

"Lots of people have been bothered by the noise – I have spoken to my neighbours about it before."

Andrea Ghirardini, 38, works in IT. He also lives in the north block but spends a lot of his time in Milan

He said: "I have lived here for two and a half years now and it has been going on ever since I can remember. Some nights an alarm goes off, some nights it doesn't.

"It sometimes wakes me up, but not always."

Police said they had not received any calls of complaints in the area. Council officials said there had been no specific complaints about the noise and that there were no alarms set by the authority in the area. They added that they were looking into the mystery.