There comes a point in a mans life when he has to get up off the coutch, walk down there act like your not scared of the name of the man, the name of the business, the reputation of the stereotype, act like an American citizen and face your fear, in the face.
Go down there, say ""hey, you have a car thats alarm goes off sometimes, and I am extremely sensitive and require complete silence every minute of everyday I cannot tolorate an ocasional blare of a car alarm... could you please take care of the problem"" Now, if the person you are talking to turns and returns with a bat, then you will have something to be scared of. Most likely he will tell you, "Sorry, we will try to take care of that... then blow you off". Then if in the future, you do have to complain in court, at least you have gone down there with your complaint and tried to settle the matter between adults.
Why you think you are a big enough threat to them because you have a complaint, you are being paranoid and ridiculous. After you have gone down there and tried to handle the situation like the man you really should be, and nothing is done, you may take another step.
What are you going to do, take them to court to sue them for an issue you NEVER brought to their attention, with no proof that this is even happening!!! Do you know what decibel the alarm is? and how do you know the car ISN'T being broken into? If the whole neighborhood is as scared as you think they are who is going to back you? You have your name and address on the court complaint, you have gone to COURT to confront some most likely really not so bad guys, without so much as a certified letter to make your complaint known. !!!
You are over reacting and need to put the sopranos dvds down and go find someone to talk to at the business about the alarm, and a psychologist about your irrational fears of Italians.