FOREST GROVE, Ore. - There's a new clue in the search for the source of a mystery whistle ringing through a Forest Grove neighborhood.
Neighbor Michael O'Brien also heard the noise last week. He said the shrill tone lasts for a few seconds, but everyone living there is stumped on where it is coming from.
"My wife was just down the hall and didn't hear it. By the time I mentioned it to her, it was already gone," O'Brien said.
The high pitched sound can be heard for blocks. People noticed it about five times last month, and as recently as Thursday morning.
Officials ruled out gas lines, utility relief valves and fire alarms.
O'brien lives across the street from a wastewater site and a cemetery. He says those are probably not the culprits either.
We took the recording to audio expert Tobin Cooley, who measured it with a sound level meter. He said he gets plenty of calls for mysterious sounds, but this one is by far the most baffling.
"It sounds like some sort of pressurized gas or air through a fitting or valve or something," Cooley said. "It's not steady state and you can't predict when it's going to happen. Those are all interesting sound features."
Cooley said he thinks the sound is originating near Gales Creek Road, as high-pitched tones don't travel very far.
"The best instrument by far is the human ear," he said. "If you can track it down and experience it, with measurements and your ears, you can find the source."
A spokesperson for Northwest Natural Gas told me that it's not a gas line, and they don't have any relief valves in the area. They say a leaking line would sound like a tea kettle, and people would smell the gas.