This is 99% invisible. I'm Roman Mars.

Mexico City, in case you've never been, is full of distinctive sounds.

There's the bell the garbage men ring letting you know when it's time to come down and throw

out your trash. On some corners you can hear organ grinders cranking out tunes for tips.

There are of course the roving Mariatchi bands. Banc, and there are the public markets where you can hear countless vendors

hawking their products. But there's one specific sound that cuts through the den a voice that if you've never heard it before

but there's one specific sound that cuts through the den a voice that if you've never heard it before, might stop you in your tracks. Tambore, refrigerators, is two-pass, the balladas, my groans, or al-a-lors,

my groans, or al-go to fear of us what went on. What you're hearing is a recording that trucks in Mexico

what you're hearing is a recording that trucks in Mexico City play on a

relentless loop.

Reporter Ted Seifer.

The crews inside these trucks are looking to buy old household items and appliances.

Basically, they're scrap metal haulers,

and the recording is their pitch to prospective sellers.

We buy mattresses, bed frames, refrigerators.

The list of appliances continues with stoves, washing machines, microwaves, and then crescendos

gloriously with this line.

Which basically means or any old metal thing you're selling.

This last bit has become the recording's namesake,

Fiero Viejo, literally Old Iron.

The recording started popping up in neighborhoods surrounding the capital city in the early 2000s,

but steadily the sound caught the attention of the internet and a growing number of amateur

...