A noise expert has confirmed the mysterious sound disturbing some residents of a northwest neighbourhood, but finding the source of the hum is proving difficult.

"It does exist. People are not imagining it," the University of Calgary's Marcia Epstein said about the noise in Ranchlands.

"It's literally a hum and it's not terribly loud, at least as I heard it, but definitely enough to lose sleep. If you heard this hum going on all night it would be very annoying."

Sounds of the city?

In June, some neighbourhood residents told CBC News the noise was causing them to lose sleep and patience. They recruited Epstein and noise engineer Richard Patching to try to find the source.

Only a handful of residents completed a survey distributed this summer on the noise, which has made finding the source difficult. But Epstein has some theories.

"One of the possibilities is this may be urban infrastructure noise…. in other words all of the energy plants, the city roadwork, the private companies that have motors running and fans running on their buildings. This may be picked up, it may be transmitted in particular ways in that area. We are looking at the geography to find out whether that is a possibility. These vibrations can be picked up by the frames of houses as well."

But that likely isn't the full explanation, Epstein said.

"There may be some involvement of electromagnetic frequencies as well. And those are very difficult to measure," she said. "Some people are more sensitive to them than others. They can interact with actual sound waves in ways that may be producing a problem. Another possibility may be underground transmission through water pipes, storm sewers. We are just not sure yet."

Need more help from neighbours

If the source is the everyday noise of living in a city, Epstein said that doesn't bode well for Calgarians.

"That's a disturbing thought because as the city grows, and it is certainly growing very quickly, there is going to be more and more of this kind of noise. I've heard from a lot of people all over the city, not just in Ranchlands, but in other places in the northwest and the southwest, indicating that isn't the only problem with a hum in the city."

Researchers need a "couple hundred" responses to the survey, including from people who don't hear the noise, in order to further help Ranchlands residents. Epstein and Patching have no funding for their research, so they are volunteering in their spare time and warn it will take longer to find answers.

The researchers are hosting a public meeting Wednesday night at 7:15 p.m. at the local community centre on the "hum."