As a general rule for airport noise, look at google earth or near map or whatever and draw a line straight along the runway centrelines from the runway ends out for about 10 miles. If you really get upset at jet noise (which is getting a lot quieter, though more frequent) avoid buying inside say 2-3 miles either side of those lines. On departure the noise 10+ miles out is a LOT less than inside that (if the departure does not involve a turn - which it usually does) and on arrival (though it depends on bizarre vectoring and arrival procedures) thrust is generally only about 20% of takeoff power and therefore quieter.
If you are really concerned, live near the Blue Mountains (Kurrajong etc). Aircraft always stay away (and are kept away) from big hills and big buildings!
Australian airports are controlled in an embarrassing manner - if pilots and controllers (as opposed to politicians) were allowed to design arrival and departure routes, there would be a LOT less noise. Unfortunately until you stop voting for them there will be no changes!!