Southampton Water mystery droning prompts more moaning
The number of complaints from residents in part of Hampshire who say they are being disturbed at night by a low-frequency noise has tripled.
New Forest District Council and the Environment Agency say they still do not know what is causing the drone that has been going on for several months.
More than 30 complaints, mainly from people in Hythe, Holbury and Fawley, have been received by the council.
Some reports have suggested it could be calls from mating fish.
But Davina Miller, from New Forest District Council, said it was not yet known what was causing the noise and added it was unlikely to be the mating of midshipman fish.
No sound detected
She said: "A number of suggestions have been put forward by the public which include dredging in Southampton Water, noise from the refinery or other industrial processes along the waterside, power cables, circling aircraft and even mating fish.
"At the moment we are keeping an open mind as to the source of the noise, particularly as low frequency noise can travel considerable distances.
"The midshipman fish is not commonly found within the inshore waters of the UK.
"As far as we are aware there are no other marine fish native to this country capable of creating widespread noise disturbance of this nature."
An Environment Agency spokeswoman said: "It could be anything. We can't set anything in stone just yet as we're still eliminating all the possibilities."
The number of complaints has risen from 10 a week ago to 30.
The council has been conducting out-of-hours monitoring, but did not detect the sound because background noise levels in the area were too high.
Ms Miller said monitoring equipment would now be deployed at a number of properties over the forthcoming weeks.
Everybody who has complained will also be asked to keep a diary to record of the dates and times they are affected by the noise.
Ms Miller said a small number of complaints had been received from people as far away as Lymington, Marchwood, Totton, Shirley, Swaythling and Sholing.
Some people believe that the noise is constant, but is particularly noticeable at night. Others say it occurs from late evening until early morning.