check your county ordinances, if there is a noise ordinance, then write a letter of neighbour of your complaint, mail it so they have to sign for it...proof they got it
then when you have proof of delivery, and a copy of your letter of complaint.......call the police again
show them your letter and proof of delivery then they can talk to them whether the offence is taking place or not and warn them of possible fines, etc if they are called back again.
I live in Ga. and did this concerning barking dogs and it worked.......ps when the cops came back the next time and rang neighbours door she answered door with a gun in her hand.......big mistake
so don't approach them yourself.......you never know