This really depends on the build. I have lived/stayed in places in the middle of dense urban areas where you essentially never hear anything (occasionally sire

This really depends on the build. I have lived/stayed in places in the middle of dense urban areas where you essentially never hear anything (occasionally sirens if the windows are open, that sort of thing), and others where you can tell when your neighbor is stirring tea. One of the factors is cost, yes, but also age of the building and materials/techniques matter. I suppose it also matters if any of your neighbors are 23 and like powerful stereos - but that holds pretty much anywhere that isn't very rural. Oh, and in dense urban/busy areas, height matters too. Living on the first 5 floors is far different than say 15+, in terms of how much street noise etc. you will hear with an open window (or even without).