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I have a month-old Dell laptop running Ubuntu. When I have it on my desk, I normally plug a stereo receiver into the audio jack, and play all sound through the receiver. But recently, I've started getting a loud hum with this setup.

The hum starts several seconds after plugging in the audio cable. The hum only appears when no application is playing any sound. When the computer outputs any kind of sound (from a music player, or audio feedback due to clicking something) the hum stops, but then the hum starts again several seconds after the sound stops.

There is no hum when I plug headphones into the audio jack - it only happens with the receiver. There is no hum when I connect other audio sources (like my phone) to the receiver.

Is there anything I can do to help narrow this down?

System info:

  • Dell Precision 7530
  • Ubuntu (installed at the factory) running kernel version 4.15.0-1057-oem
  • Mate desktop, version 1.20.1-2ubuntu1
  • Realtek ALC289 audio chip
Mike Baranczak
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    I would ty a different cable between receiver and audio jack. – WinEunuuchs2Unix Oct 14 '19 at 22:20
  • Please click [edit] and advise the results of the above suggestion, as well as what happens when you run your laptop without the charger plugged in. Please don't use Add Comment; instead, use [edit]. – K7AAY Oct 14 '19 at 23:57
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    It seems to be a typical "Ground Loop" issue. You have to check if the electrical ground connection of your home electric system is 100% OK. BTW, Sometimes a Toroid Ferrite Filter is useful. You have to put it, on the audio cable, near the laptop audio output connector. – Juan Oct 16 '19 at 14:33
  • Unplugging the laptop power cable has no effect. – Mike Baranczak Oct 16 '19 at 15:19
  • @Juan How exactly should I check the ground connection? – Mike Baranczak Oct 16 '19 at 15:20
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    Sorry!!! If you use the laptop with its internal battery, only, then it isnot a "Ground Loop" problem. I think your best option is to use an external USB Audio interface. Something like this: https://cdn11.bigcommerce.com/s-wjhy8fxg5c/images/stencil/1280x1280/products/31985/48676/ARX_USB_IO__53760.1562864512.jpg?c=2&imbypass=on – Juan Oct 16 '19 at 19:09
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    No it isn't a 'ground loop'. Read the OP's message again. The hum appears a few SECONDS after the sound stops. This appears to be a change in the way the audio output stage is operated. The output seems to be turning off/going high impedance which allows the hum to be picked up in the equipment. I now have this problem on my desktop machine running Kubuntu 20.04 but it was fine for years before on earlier versions. – John Lawton Nov 16 '20 at 10:30
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    This may be the same root cause as another issue related to putting audio output device in power save mode: https://askubuntu.com/questions/1230833/annoying-click-popping-sound-on-ubuntu-20-04 . Try the solution mentioned there. – raj Nov 16 '20 at 11:06

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