OK, now listen to this.

Any idea what it might be? You may have driven or walked on it before. Sound artist Jodi Rose recorded it with contact microphones, and then she loaded up the audio to a website called Aporee.

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Aporee is a crowdsourced sound map with audio from all over the world. It's as if Google Maps had audio. You can hear recordings made in different places by clicking on locations where sounds have been uploaded.

So, what's on the map from California?

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Aporee has many recordings one might imagine when thinking of the state's sound profile -- nature audio like waves crashing in Santa Barbara, sea lions on the Sonoma Coast and birds chirping in Point Reyes. But there are also urban soundscapes -- downtown San Francisco with street performers and cable cars, a casino in San Diego, the 101 freeway in Los Angeles, a mall Starbucks.

Some contributors have focused on capturing sounds of particular things -- oil derricks, irrigation pumps and sprinkler systems. Often the recordings are of the kind of background noises many of us ignore or tune out altogether.

Aporee was created by Berlin-based sound artist Udo Noll. He wanted to make a site where people could share audio and preserve it for the future. The website is part archive, part art project, part community space. The sounds are free to listen to, download and remix under Creative Commons licenses.

All of the places on Aporee have been captured visually at the very least by Google's cameras or satellite images. But most of these locations have never been documented sonically.

Sound is often overlooked, Noll says, which is a shame because audio can transport someone in different ways than images. “Sound puts you right at the place,” he says, and “you have a kind of landscape that opens up.”

Most of Aporee's audio clips are several minutes long. A majority are soundscapes, kind of audio snapshots. When you listen to recordings like these, Noll says you are “sharing ears” with the person who gathered the audio.

Noll has always been fascinated with sound. When he was growing up in Berlin, his aunt had a big old radio that could pick up distant signals. There was a dial on the front, a magic eye Noll says. It would display where the frequencies were coming from -- places around Germany, France, Eastern European countries still under Soviet control, and far-off cities like Daventry. It's the place in Northern England where the BBC Empire Service built its first radio antenna.

Noll would tune in to these frequencies and listen. In a way, he says, those radios were the first sound maps.

Karel Sidorjak records sounds that grate on him, like the crash of bottles at a recycling center. (Sam Harnett/KQED)

Anyone can upload audio to Aporee. There are musicians like Jodi Rose, who did the Golden Gate Bridge recording at the top of the story, and people like Dan Dugan. He invents audio equipment and makes nature recordings, such as a dawn chorus of birds in San Francisco's Presidio.

Many contributors, though, are just hobbyists, recording sounds the way one might take a picture -- amateur “phonographers,” like Karel Sidorjak.

Sidorjak is a carpenter by trade, but he carries around a small inexpensive recorder. At first he was gathering lots of nature audio—birds, creeks and ocean waves. Now he is more interested in urban sounds. He goes out to record BART stations, industrial noises and the “horrible music” at Home Depot.

I went with Sidorjak to see a phonographer in action. We planned to visit one of his favorite places to record in Berkeley. First, though, we had to gather up his recyclables.

Sidorjak had been saving bottles for months. They are mostly Pilsner Urquells. It's his hometown beer. Sidorjak is originally from Pilsen, Czech Republic. As we poured the bottles into plastic bags, they made a deafening crash.

"That is a nice sound, right?" he asked and laughed.

We took Sidorjak's bottles to a nearby recycling center. He had his recorder on, and so did I.

Sidorjak wants to document the gritty sounds that fill our urban landscape. Over the din of crunching glass and plastic, he said, “The sound environment we spend a lot of time in is just plain bad."

Sidorjak has made several recordings in the recycling center. He always notes how little money he makes returning the bottles. I like this trip the best --it's something about the songs he captured playing on the radio in the background.

For Sidorjak, Aporee is a place to put the different sounds he gathers -- ones that grate on him, like the crash of bottles or music at Home Depot, and ones he loves, like the creeks behind his house.

So far, Aporee has almost 30,000 recordings, about 63 days of sound. It's actually not that much, says founder Udo Noll, especially compared with something like the number of tweets sent out every day into the ether.

What sounds are we missing, Noll wonders. Which ones will vanish before we ever hear them?

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