Rangiora couple Ron and Liz Kautz want everyone to know they are hearing things.
And they want to hear from anyone else in the district who has noticed a continuous low-pitched hum that refuses to go away.
"We've been hearing a hum for over a year now," Mr Kautz said.
"It is affecting our sleep and we can hear it almost any time if the ambient noise is low enough."
Mr Kautz said the hum sounds like a "heavy truck engine idling in the distance".
"The frequency is about 80Hz and it feels like a pressure wave in our heads."
Mrs Kautz said the hum gets in her head.
"It's such a low humming sound. It's vibrating in your head and seems to follow you around."
The couple suspect the hum may be coming from the Daiken fibreboard manufacturing plant north of Rangiora that runs continuously, 24 hours a day.
"It has the same tone. If you stop outside that place you will see what we mean," Mr Kautz said. "It may be an air conditioning plant or extractor fan that's resonating."
The couple has approached Waimakariri District Council, but noise control officers have been unable to shed any light on the cause of the noise.
Council environmental services manager Les Pester said the Kautzes' complaint was being taken seriously and investigations were continuing.
"We can't pick up the sound ourselves and we're going through a process of elimination," he said.
"It's a mystery at this stage."
A Daiken New Zealand Ltd spokesman said the company was unaware of any noise complaint "as we have not been approached in regard to this issue before".
Daiken would "happily help with any investigation that is required", he said.
Mayor David Ayers has referred to the hum in his regular blog, calling for anyone who hears it to contact him. Two people have replied saying they frequently hear a "very low level humming noise".
Mrs Kautz said they would like to hear from others.
"If we could find out where it's coming from and what's making the noise it could be an easy fix," she said.
Mr Kautz said they were sure they weren't the only ones being annoyed.
"There may be others out there who are suffering because of this.
"The more people who put their hands up the more chance we have of getting it resolved."