Thats not a problem as long as your Ammunition does not leave your boundry i.e goes out of your garden into theirs, tbh a CO2 Pistol Rep clacking away would draw more attention than a conventional Air Rifle would so if they weren't bothered by that then you needn't worry but again, aslong as you keep it legal, have a decent back stop and don't make a racket at an unsociable hour theres little they can do even if they don't like it.