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Any powered external speakers I connect to my laptop make a buzzing noise when my laptop is plugged in. I also have battery-powered noise-canceling headphones that make the buzzing if noise canceling is enabled. Quick summary:
Laptop Speakers Buzzing noise?
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Battery (any) No
Plugged in Internal No
Plugged in External, plugged into wall outlet Yes
Plugged in Headphones, active noise canceling enabled Yes
Plugged in Headphones, active noise canceling disabled No
Plugged in Earbuds, passive No
The buzzing is louder if my display brightness is low, and especially loud if the display is turned off.
The buzzing happens with any power outlet: I've tested it in several buildings in two different cities. I have also tried plugging the speakers into a separate outlet from the laptop (one connected to a different circuit breaker), but the buzzing persists. This leads me to believe that the issue isn't due to some sort of ground loop (and this is supported by the fact that the buzzing happens with the battery-powered noise-canceling headphones).
The volume of the buzzing does not change if I adjust the volume on either my computer or my speakers.
The buzzing stops if my CPU is at 100%. For example, if I run two instances of yes
(one for each CPU core), I don't hear anything out of the speakers.
I recorded a segment (you'll probably have to turn your volume up) of the buzzing noise with my phone and performed a frequency analysis:
The peak just to the right of the 100 Hz line is centered at 120 Hz, which is double the frequency of the AC power here.
Why does this happen and how can I fix it?
I'm betting your PC is sending extra power to them when it can spare it, and it translates as buzzing. I don,t think you can fix it... Doesn't sound like something you can adjust. – Ariane – 2013-01-13T21:14:04.887
1+1 for extensive testing and very detailed question – That Brazilian Guy – 2013-01-13T21:23:26.927
You mention display brightness. Do you mean an external display that is plugged into the AC outlet? If so, that's quite significant. In any event, it sounds like a "hum loop". What type of laptop do you have, and does it have a 2-pin AC plug or a 3-pin AC plug? – Daniel R Hicks – 2013-01-13T21:36:52.777
How are your noise-cancelling headphones powered? – Daniel R Hicks – 2013-01-13T21:38:25.287
@DanielRHicks: The laptop's display, not an external one. It's a ThinkPad T500 and it has a 2-pin AC plug. – Snowball – 2013-01-13T21:38:34.670
@DanielRHicks: The noise-canceling headphones are battery powered. – Snowball – 2013-01-13T21:38:55.933
Does it still buzz at about the same volume if you unplug the AC adapter and turn the plug around 180 degrees? – Daniel R Hicks – 2013-01-13T22:32:44.453
@DanielRHicks: I don't notice any difference with the AC adapter plugged in the other way around. – Snowball – 2013-01-14T05:29:32.523