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I've seen a lot of thread about this question but it seems that it doesn't suffice what I'm looking for.

So this what happened:

My wall outlet has three sockets and all of which was used. The bottom part was used with laptop, the center was used with lamp and the upper part was used with cellphone. As I got up, I noticed a hissing noise on the wall outlet. As a normal person I was bothered but then my curiosity struck so I tried to unplugged the charger of the cellphone then immediately, the hissing stopped. I tried to plugged it again and then the hissing started back.

I don't know if that was caused by interference of the current or what? Maybe there's a need to fix the wall outlet? I don't know if it was really caused by the cellphone. That was the only thing that I unplugged so I supposed it was.

I need to be enlightened. Thanks!

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    Your phone charger is a transformer. It's apparently vibrating a bit while doing its thing, possibly due to cheap components or a poor design. At any rate, this isn't about your outlet or line power (and therefore isn't about home improvement). Have you tried that charger in another outlet or another building? – isherwood Mar 9 '17 at 17:31
  • @isherwood Yes I tried it with another outlet and it was not producing a hissing sound. What do you think? – Dean Mar 9 '17 at 17:34
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    You should probably get the outlet checked just in case. – Trevor_G Mar 9 '17 at 18:04
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It's rather unlikely the cell phone charger is a transformer these days. Nowadays, they are switching power supplies.

While it's possible to build a switcher with .99 power factor, the cheapies have really weird power factor with crazy harmonics, and at much higher currents than you'd expect. This creates EMF (literally, electro-motive force) which can make things move, i.e. vibrate.

I could see that being a "canary in the coal mine", causing weird effects on an outlet that's already marginal. A tight good outlet should not do that. If that's a NEMA 1 type receptacle, it's gotta be an oldie. It may simply be a wire that has loosened over the years, or an internal component that has broken.

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