Personally, I think chickens are really quite. Much quieter than a neighbor's donkey! (Who we love, but still, that thing can produce a hee-haw that carries a long way across these mountains.)
My chickens are certainly quieter than the airbnb guests on the knoll behind us whose renters seem to have never outgrown their college fraternity days. They're a good distance from us, but again, that noise carries across these mountains and they stay up a lot later than our chickens. But we don't complain. We figure that if the owners want to clean up after and deal with partying renters, then they have it much worse than us!
Unless the noise can be proven to be physically damaging or is consistently going past "acceptable" hours (say before 6-7 am and after 9-10 in most cases, but this would exclude music venues, bars, etc), I don't think 'noise' is a valid reason to pitch a fit.
Are there any chicken decibel studies so you can show that they're about the same or quieter than most human voices? That might help! I wish there was some way that the people who complain the most got the least amount of attention, but unfortunately it's the opposite. I really do massively applaud you for sticking to your GUNS (hehehe) with this issue!