Diagnosis
A very faint hum or buzz from the internal relay is normal when the plug is actively switching or carrying a high load. A loud, persistent buzz is not.
How to Fix It
Check what's plugged into it. High-power devices like space heaters, hair dryers, or powerful motors can cause more audible relay noise. Try plugging in a simple lamp to see if the noise stops. If it does, the noise is load-related.
If That Didn't Work
If the buzz is loud and constant even with nothing plugged in, or you hear crackling, the internal relay may be faulty. Unplug it immediately and contact TP-Link support for a replacement—do not continue using it.
Heads Up
These plugs have a physical, mechanical relay inside that clicks and can hum. It's part of the design. However, any smell of burning, sparking, or a loud, aggressive buzz indicates a failure and a potential fire risk. Replace it.