South Vancouver Island residents are puzzled by a recurrent loud rumbling noise that some liken to the sound of a jet, and others to an earthquake.
Gordon Head resident Verna Laliberte said it can last for up to 30 seconds.
"It's like a jet taking off."
Lolly Wilkinson, who lives near Esquimalt Lagoon, said the sound started about three weeks ago and is so loud she can hear it over traffic.
She said the noise varies, but lasts for five to seven seconds before diminishing.
"It's ominous," Wilkinson said.
Both women live near the water, but Stephan Mazzotti, seismologist at the Pacific Geosciences Centre, said he has received reports from residents in Gordon Head, Fairfield, Central Saanich, Elk Lake and Langford.
One woman recorded the times the rumble was heard, but Mazzotti said those times do not coincide with any seismic activity, adding an earthquake would have to be fairly large to be heard.
Other suspects -- blasting in Saanich, commercial aircraft on new flight paths and military detonations on Bentinck Island near William Head -- were also ruled out, as was seismic testing being conducted by a research vessel 250 kilometres southwest of Vancouver Island.
Laliberte mused that the noise is coming from the American side, but in Washington state, residents are wondering what the Canucks are up to that's causing the racket.
Tom Callis, a reporter at the Peninsula News in Port Angeles, said they've been reporting on the phenomenon for weeks, with some instances noted as early as April of this year. At that time, Hubert Genest, spokesman for the Canadian military's Joint Task Force Pacific, said the noise could be from U.S. military aircraft returning from manoeuvers on Vancouver Island.
That theory was later contested by a Canadian military spokeswoman.
"It's a mystery," Mazzotti said.
Or is it? Kimberly Martin, spokeswoman for the naval air station on Whidbey Island, believes she has the most likely explanation.
She said summer runway repair has left only one runway available, one that sees aircraft moving in Victoria's direction.
That's not unusual in the summer months, Martin said, but what's different this year is that the U.S. is phasing out its EA6B Prowler fighter aircraft, and training personnel with Boeing EA-18G Growler fighters.
"The EA-18G Growler has a different sound -- it is possible that's what they're hearing," Martin said. The aircraft is conducting touch-and-go exercises where the plane practices quick touchdowns, then accelerates for a fast takeoff to simulate the effect of aborting a landing on an aircraft carrier.
She believes that explains the two distinct descriptions of the sounds as well. The five-to-seven-second noises would be from the touch-and-go exercises, while those reporting a 30-second span are likely hearing the fighters move in a horseshoe pattern toward and then away from them.
"How it sounds will depend on where you're situated in relation to the aircraft," Martin said.