Airport expansion, or addition of new runways etc. are usually a tediously long process, and usually with a lot of community feedback and approval etc. (at least, here in Australia it is). Not something that can happen overnight without anyone knowing.

Flight path changes are more common. But then again, those are usually departure pathways. The worst noise issues are on final approach or on the takeoff run on runway heading, which rarely change. Most turning points are above 1000ft AGL where the noise levels are a lot less.