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?
Best Answer
Sounds like a power supply issue. In a computer's power supply, a constant voltage is maintained by a component that switches the power to a storage capacitor on and off very rapidly.
I'm willing to bet that what you're hearing is the voltage regulator switching on and off. When you do anything that requires additional power (i.e. turning up the brightness up, or running the CPU at 100%) the regulator is kept on for a longer period during the cycle. When you use less power, the regulator "on" time is shortened. This switching is generating electrical noise which is being amplified by your speakers.
Power supply manufacturers go to great lengths to minimize the electrical noise generated. It's possible that your power supply may be faulty. Do you know anyone else with a Thinkpad? If so, see if you can reproduce the issue when your laptop is plugged into their power supply. If it's still happening, it could be an issue with the motherboard. If the ferrite core has become detached from the end of your laptop's power cable, that could also be the cause.
There's a chance that a driver update could resolve the issue. It's a small chance, but worth a try. Assuming you're running Windows, download and run Lenovo's ThinkVantage System Update utility and install any available audio driver updates.