Which of the following can create intermittent loud roaring or buzzing AC line interference?
Arcing contacts in a thermostatically controlled device
A defective doorbell or doorbell transformer inside a nearby residence
A malfunctioning illuminated advertising display
All these choices are correct✓Correct answer
Explanation
All three share the same mechanism: a repeatedly breaking contact produces a rapid succession of small arcs, and the broadband energy from those arcs is heard as intermittent buzzing or roaring across a wide range of the receiver's tuning.