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My wife leaves her laptop charger plugged into a wall outlet. As soon as she connects the other end to the laptop (meaning AC is actively flowing through the plug to the laptop), it makes a strange hissing noise.

Is this something to worry about? Is this the outlet itself, or a symptom of a bigger problem?

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The laptop makes a hissing noise, or the wall outlet makes a hissing noise? – Karl Katzke Aug 21 '11 at 2:53
Laptop power supplies will often make a harmless hissing noise. Be sure that it is the laptop power supply, and not the wall outlet. If the wall outlet is doing it, it is very dangerous. – Brad Aug 21 '11 at 14:43
Hissing sound in the outlet is something to be addressed ASAP, but aware that it might be the charger itself - electronics.stackexchange.com/q/14256/3552 – sharptooth Aug 22 '11 at 6:14
up vote 9 down vote accepted

Does the noise happen when another item such as a lamp is plugged in the outlet? If so, the outlet is bad and needs to be replaced or has loose wire connections. If it doesn't make noise with anything but the computer power supply, it may be the transformer of the power supply making the noise.

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I have noticed that sometimes computer AC/DC power bricks can make a faint hissing noise. I would recommend you try other devices in the same outlet, OR move the computer to another outlet and see if you get the same results. I am banking on the AC/DC power brick making the noise. – Josh Aug 21 '11 at 13:12

If the circuit makes a 'hissing' noise as soon as load is applied, then you definitely should check that outlet for a problem.

Shut off the power at the breaker. Confirm that the power is off using either an electric light plugged into the outlet, or by using a Non-contact voltage tester. Unscrew the faceplate of the outlet, then unscrew the outlet. Examine the wires for heat damage or signs of arcing. I'd probably just go ahead and replace the outlet.

This is definitely something you should worry about; I'd expect to see something like this:

Heat-damaged outlet

If you don't feel comfortable doing that, call an electrician.

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Check both outlets before tinkering. While its unlikely in a office or bedroom, your outlet could be a split. Always check both outlets for voltage. – Chris Cudmore Aug 21 '11 at 14:37
@Chris: Second this. I have a split outlet in the room I use as an office. I needed an additional line run and the additional cost to run an extra wire to it was only a few bucks, I had them do it that way. There is one paired breaker in the box that controls both sides, though. – Loren Pechtel Aug 21 '11 at 17:13

If the problem hissing is from the transformer than this may be caused when the copper coils are too close or have lost their shield coating. If this is your problem, you should consider replacing the item because it is extremely unsafe. Overall, just replace the item. It is unwise to work with loaded circuits.

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@johnnyBoy314- keep your answers to the point. Always remember to understand what the question you are answering. – ojait Sep 20 '15 at 0:34

If it's a spur it's most likely known as a broken spur which mean there's no power going to one and all the power going to the other which is to much power which majesty's the hissing noise it's extra voltage trying to pass through. If it's not a spur it's either heat damaged or the front plate needs replacing either of these problems need fixed and fast also if the flex has been lengthend by a convection block it must be the right amp and can't be used as a permanent way to lengthen the flex

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Please proofread this post and fix the typos, for example "which majesty's", "convection block". – Niall C. Dec 31 '13 at 5:43

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