Mexico is a really loud country. However, that's not necesarily a bad thing.
The first thing you'll notice coming to Mexico is how much Mexicans love to celebrate. It doesn't really matter what the occasion is, but Mexicans are very happy to gather together, pull together some food, some bottles of Squirt and tequila, and crank up the music. Add in some dancing, perhaps a piñata, and you've got yourself a real celebration.
But not all of the "noise" in Mexico comes from parties. Every church in Mexico has its patron saint, on the the feast day of that saint, the church offers a big celebration for the whole community. This generally begins early in the morning (sometime "early" means 4:00 am!) and continues throughout the day, usually with cojetes—fireworks with no light display but only the bang. When it originates from the church on the next block, you bolt awake from your slumber, remember what the occasion is, and the drift back to sleep. The cojetes continue, every fifteen minutes, throughout the day. (Mexican dogs frequently hide themselves, shivering, in a closet or under the bed.)
Perhaps my favorite "noise" comes during the course of a normal day. The garbage collectors pass through the neighborhood (every single day except Sunday) ringing a large bell as a signal to bring out your trash. (Unlike municipal waste disposal services in the United States, in Mexico this is provided by private contractors who each have a neighborhood as their turf.) When the garbage collector arrives, you give him (usually a him but sometimes a her) a few pesos for hauling away the trash. Since you can hear the bell from several blocks away, you always know when to put out the trash.
In the evenings are vendors with small pushcarts that pass through the streets—some selling roasted sweet potatoes, some with ice creams and popsicles, some with just novelties and toys aimed at children. Each one has a particular bell or whistle or chime, so you know from a distance who is coming down the street. My favorite is the knife sharpener—he has a pedal-operating grinding stone with which he can sharpen your kitchen knives for a few pesos each, and he blows a metal whistle with a lonely, ethereal tone that I find haunting.

As I discovered when I first came to Morelia, there are bread sellers who drive through the neighborhood in the evenings selling bread from their car or truck, and they always play the song "El Panadero con el Pan" (The Baker with the Bread).

Another daily service with its own song is provided by the scrap metal dealers. They drive their trucks through the city with a recording to alert you to their presence in your neighborhood. According to the recording, they're interested in purchasing any number of household items that you're looking to get rid of. (This recording was made in 2004 by a scrap dealer who tired of using a megaphone to advertise his presence, so he engaged his young daughter to make the recording—he drew pictures of the items so she could easily remember them.) The recording was passed around by being duplicated on cassette tapes, and today you will hear it in every Mexican town.
The text of the recording is "Se compra colchones, tambores, refrigeradores, estufas, lavadoras, microondas o algo de fierro viejo que venda."
In English, it's "We’re buying mattresses, metal drums, refrigerators, stoves, washing machines, microwaves or any old metal things that you’re selling.” This has become an iconic part of any Mexican city, and the recording has been remixed by DJ Ariel Style and even sung in an operatic style.
Add all of this to the sounds of traffic, of boomboxes, of the lady selling tamales door-to-door, and you have a blanket of sound that's a little overwhelming when you first arrive, but after becoming acclimated, it becomes the very best kind of blanket—one that soothes and reassures that life is good.