Britain's biggest onshore wind farm, in North Devon, could be operating well above permitted noise levels in every location where readings were taken, a new report claims.
Residents have called on North Devon District Council to shut down the facility at Fullabrook after a report commissioned by the authority said all 22 turbines could be exceeding set limits.
The plant's operator has released data from a monitoring exercise which showed five of the 12 measured locations were noisier than Government maximums.
But in a study to verify the data, acoustic specialists say the firm has not factored in an extra audible "hum" which would push all the readings above the maximum.
Bob Barfoot, North Devon chairman of the Campaign to Protect Rural England (CPRE), said the results were not unexpected.
"It was quite obvious to everybody that they would exceed the limits," he added. "These Vestas machines are too big and too noisy to be used on shore and this has been proved by Fullabrook."
Neighbours have repeatedly argued that the permitted maximum of 40 decibels (db) or 5db above background noise is still much too high.
Nick Williams, who has been prescribed anti-depressants to help him cope with the effects of the plant, lives 450m away and can see seven turbines from his window.
The 53-year-old told the Western Morning News the sound was like a "tumble drier" and often at its worst on clear winter days.
"They have woken me up two nights in a row – it is not acceptable," he added.
"I think the council should turn them off – if you built a house and broke the rules they would come down on you like a ton of bricks."
The testing was carried out earlier this year by ESB International, in order to satisfy the council that it is not breaching planning regulations.
Two reports into noise assessments around Fullabrook have been released this week.
A compliance assessment report by ESB showed that broadband noise levels – the "swooshing" of the blades – recorded at four locations were above the limits set out within the planning consent, by up to 1.9db in certain wind conditions. The report says the operator intends to work with the manufacturer of the turbines to ensure they return to acceptable levels.
Meanwhile, North Devon council has also released an independent report, by Robert Davis Associates, to verify ESB's assessment study.
Both reports said that "tonal noise" was measured, at Binalong, Crackaway, Beara and Patsford. The verification report said under planning conditions this attracts a "graduated penalty of up to 5dB". "The analysis presented to date does not include any correction to measured noise levels to take account of audible tones," it added. "Since noise levels at all 12 survey locations are within 5dB of the noise limits at some wind speeds the addition of a penalty for tonal noise could result in noise at all locations being shown to exceed the limits."
North Devon council is "seeking further clarification" on the tonal noise issue and said ESB has commissioned further work to quantify the "degree by which tonal noise is a feature".
ESB said engineers from Vestas were investigating solutions to the problem.