Only a leading edge dimmer causes a buzz in transformers and in itself. When a transformer is operated on a normal non-dimmed AC cycle, it is quiet because it turns on “softly” when the AC starts off from zero volts. On leading edge dimming the transformer experiences a sudden electrical and mechanical “shock” when it receives the sudden very high voltage and corresponding inrush current. A trailing edge dimmer and transformers being dimmed is quiet because the dimmer and transformer “thinks” it operates with a normal non-dimmed AC cycle – there is no sudden high voltage or inrush current that “shocks” the load
