A phantom hum plaguing North Shore residents has scientists puzzled.
Massey University is investigating reports of a humming noise which can be heard by some, but not others.
They have dubbed it the Unidentified Acoustic Phenomena.
It all began when a North Shore woman complained to environmental authorities about a constant hum she hears when she is at home.
After receiving no explanation, she decided to enlist the help of Massey University.
Dr Tom Moir says since he has begun investigations he has been inundated with similar complaints from people in the area.
He says the sounds can't be confused with tinnitus or other ear problems because a lot of them don't hear the noise once they have left the house.
Moir says the noise has been likened to various others such as a motor under the ground and a constant annoying humming noise.
He says one possible explanation is that microwaves in the atmosphere trigger hum-like sounds within people's ears.
Moir says the other possibility is that it is a real noise that only some people can detect.