Did you hear it? Between 10AM and 1PM on Monday, some West L.A. residents were jarred by a series of piercing noises near Barrington and Exposition Boulevard. It sounded like a miter saw cutting through the center of the earth, or maybe a new grindcore band.

The real culprit? Metro.

Ahead of construction for the remaining portion of the Expo line, Metro hired acoustic consultants ATS to do some noise tests near the site of the rail line. In fact, they took specific measurements for a pair of sound studios that probably have the most to worry about. But ATS didn't set out to mimic the sounds of a train. Instead, they just wanted to produce a really really robust signal, one that could easily let them measure how well these buildings were soundproofed.

So they basically whipped out a stadium-sized PA system. They set up four 1500-watt Dynacord Cobra speakers to deliver a multi-frequency noise at 100 decibels. They tested a handful of these noises in minute-long bursts, and according to audio specialist Alec Ernest, "It was shockingly loud every single time."

Take a listen.