"Yesterday (Sunday) there were only about 10 turbines operating but the noise was a constant roar like a speeding truck passing next to us that never went away.
"The winds were northwesterly and there was heavy cloud cover," they wrote.
Don and Shirley Nelson, who live nearly a mile away, said they could hear the noise inside and outside their home on the eastern side of the ridgeline.
Jonathan Rowell, who lives two miles away, said he could hear the turbines in his home.
Others who signed the letter live between a half mile to three and a half miles away.
In their own letter, the Nelsons said they heard the noise between Saturday morning and dusk Sunday.
"We decided to check with our neighbors and friends on the east side of the mountains to see what they had witnessed," they wrote.
They said they had heard that there are even more than those who signed the letter who heard the noise.
The letters were also posted on the Lowell Mountain Talk blog.
Green Mountain Power, which is completing start-up of the 21 turbines 459 feet tall, reacted to the letters of complaint. "The Public Service Board requires us to meet certain sound levels," stated Dorothy Schnure, spokesman for GMP.
"As part of our permit, we have protocol for responding to complaints. People who have a complaint should contact us because we want to know about it," Schnure wrote.
"If there is an issue, we will address it."
The state utility regulators on the Public Service Board granted a certificate of public good last year to GMP for the wind project called Kingdom Community Wind. Acceptable noise levels are detailed in that certificate, and GMP is required to shut down turbines when they exceed those levels.
The PSB has also approved a noise compensation plan for neighbors of the wind project.
The plan requires the neighboring landowners to demonstrate that their property is experiencing project-related sound levels that exceed 45 decibels over an hour or 30 decibels in a bedroom.
The compensation plan attempts to address complaints that indicate that noise would prevent landowners from developing their property for new residential development.