Seems that many airports in the US have some kind of noise abatement procedure, yet there's no standard and reliable way (that I know of) to learn about them. The Chart Supplement usually gives just a phone number. A few airports mention it on a web site, or a hard-to-read sign when approaching the runway. I understand these are usually voluntary, but aren't they still important enough to be captured and published the same way that other data is disseminated?