Seamos buenos vecinos. Rechace por favor la música. Gracias.

You can always try.

Being mexican they don't speak English very well ...

I know a lot of people born in Mexico who speak English excellently. The two things don't necessarily go together. 

However, I feel for you. I've had to call the cops on noisy neighbors, too. Finally, after two or three visits by Sheriff's Deputies, they got the picture and started behaving.

But you say you were threatened. That's illegal. I'd report that to the Sheriff's Department and see if that makes any difference. 

An old girlfriend of mine is Chinese. On the phone, you'd never have any clue, in person people just could not match the face with the voice. When we were out, and someone would try picking her up or to sell her something, panhandlers...whatever, she would slap on an accent and do the whole giggling girl covering her face, I soo soo solly, No speak Engrish, Herro good day.... having seen that act work so many times... I spot it all the time.

yeah I know the dumb girl act. but it's not that I think they are dumb because they don't speak English or that they're even acting it's just they don't care or get it. they feel they have a right to blast loud music from their car all day long and that I shouldn't be allowed to go outside my home and expect not to be assaulted by what they call music. If I want to open my windows or step outside I can't do that without that happening on a regular basis and they use not being able to speak English as their excuse, "oh I didn't understand or I didn't know."  I don't open up my windows and blast music or leave my car running with obnoxious music that makes their own dogs hears bleed and it's 99 cents now to buy a cheap headset, but they prefer it if I call the sheriff. So I document when it happens and I keep a written and digital record every time. If they want to act stupid then I'll treat them in kind, like they're a wee bit slow.