For weeks, residents of Omagh in Northern Ireland have been reporting a mysterious humming noise that, according to one city council official, is causing a "significant degree of discomfort." Thus far, experts have been unable to identify the cause of the low buzz.
Possible sources include air conditioning or power lines but the electric company serving the area hasn't solved the mystery either.
"It's possibly related to weather, but I think the honest point at this stage is that we don't know the actual origin and we have to be able to try and establish the facts first before we can secure a solution."
Additional specialist equipment will have to be used to further investigate the source of the noise, Mr Donnelly said.
Others have suggested it could be a "flying saucer."