If its after 10pm it is a noise violation.
I had something similar happening when I lived in NY (right across from CT

) and if it happened after 10pm I would call the police and file a noise complaint. My roommate left a note in our neighbors mailbox and said something to the effect of "you may not be aware by the honking of car horns by your visitors is very disruptive to your neighbors. Would you be so kind as to speak to your visitors and ask that they refrain from honking the horn before 9am and after 9pm?". The honking then stopped. We thought maybe they began to feel embarassed between police reports and then the letter.
good luck.