One source of noise is poor grounding in the house wiring. If the ground potential is too high in one outlet relative to another, that can induce ground loops that create noise. If you have very little noise in your environment, I'd likely attribute it to superior grounding techniques during construction. Good grounding shunts EMI/RFI to the ground before it gets to other components. RFI is less of a factor than it used to be due to the demise of radio stations, but LED lights still can be a particular problem.