Whining noise from multiple sockets ?

[LewisM]

Hello, I fitted some extra sockets in a bedroom two years ago, and the customer has said that 2 of the sockets make a high pitched whining noise, all tested at the time readings fine etc, I've attached a video, doesn't sound like arcing to me as it's not a crackling sound? I've told them not to use the sockets for now until I can have a look on Sunday, I can't see how two sockets could have gone faulty any ideas?

 

[pc1966]

That looks like a USB style charger, they often make a whining noise.

Get them to try a lamp or something else plugged in to be sure.

 

[pc1966]

Or try the white plug thing in a totally different socket.

 

[LewisM]

They said work fine in a different socket, other
socket has a TV plugged into it

 

[loz2754]

That's definitely USB charger hum, probably more audible in this socket as it is reflecting off the hard surface just below it.

 

[LewisM]

Well went there today, everything tested fine ZS wise L-N L-PE however voltage was 251V, the charger wasn't making the noise when I was there (as usual), they said it happens more at night, I've left my fluke there and told them to plug it in when the charger makes the noise and send me a picture of the voltage.

 

[KWCFC]

Mate that's the plug itself that they have plugged in. Them cheap things always start whining after a while. My phone charger is always doing it.

 

[pc1966]

Also it might whine once the phone is charged and the load drops, so only later on or unplugged.

A lot of switching converters can vary the mark:space duty cycle to regulate the power over a moderate range and switch in the 100kHz or more range so are inadudible, but when the load drops down they can't reduce the "on" time enough so start to operate in a burst mode and that might put the burst rate in to the human hearing range.