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I have a desktop PC running Ubuntu 12.04 with externally-powered speakers connected to the "front" and "rear" speaker jacks on the rear panel of the motherboard. Over the weekend, the front panel of the chassis got bumped in the area of the mic/headphone jacks (there was a cable plugged in to the mic jack at the time), and the speakers started hissing.

Sound/music still plays out the speakers, but it's not pleasant to listen to because the hissing is always audible.

I've rebooted and the hissing persists. I've removed both the "front", and then the "rear" speaker connectors, but the hissing is present on both sets of speakers. I've traced the cable from the mic/headphone jacks back to the motherboard and removed the connector (marked "HD Audio") from the header; when powered back up the hissing was still there.

What other troubleshooting/corrective steps do I need to take to get rid of the hissing?

Edit: The problem is not with the speakers, it is with the computer:

  • When I plug headphones into the front-panel headphone jack and the rear-panel "front" and "rear" speaker jacks, I still hear the hissing in the headphones.
  • When I connect the speakers (both pairs, one set at a time) to the headphone jack on my laptop, they work just fine -- no hissing, crystal clear.

Edit in response to Tog's comment re: playing with mixer settings:

  • Muting "master" turns off the front speakers, but not the rear. I can't get the rear speaker jack to go off; any speakers connected are always hissing. (I swapped cables going to front/rear, and the problem stays with the jack, not the speakers.) Of course, I don't see anything in alsamixer labeled "rear".
  • Nothing else has any effect (except that muting "front" and "surround" turns off the front speakers as expected).
  • I double-checked that disconnecting the cable from the front panel to the motherboard kills sound to front-panel headphones.
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  • Well this seem like a realy easy call. You've said it yourself - the jack socket was physicaly damaged and the noise started to interfear with music. There is probably a little short circuit causing the noise. It is affecting the sound device in a feedback. Are you using integrated sound card or a pci-e one?
    – mnmnc
    Dec 20, 2012 at 19:35
  • @mnmnc: I'm using integrated sound. The thing that puzzles me is that the interference continues when I physically disconnect the front-panel card that may have the short-circuit.
    – bstpierre
    Dec 20, 2012 at 20:14
  • Open your mixer/volume controls and mute all of the inputs and any unused outputs. Does this make a difference?
    – Tog
    Dec 26, 2012 at 12:35
  • @Tog: see latest edit
    – bstpierre
    Dec 26, 2012 at 13:30

3 Answers 3

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The issue means is very hard to be accurate for a solution without seeing it, plus, I don't know of any real tests.

It is either the cable or the speaker itself.

Try and see both - does the cable (the connection to the speaker) look OK and is still plugged in correctly. try and look at the speaker, even a tiny little tear means it is broken.

The only way to test the speaker would be to take a CD player, plug a stereo cable with exposed ends and press them against the on board speaker to see if the problem persists (ruling out speaker or cable).

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  • The speaker and cable are ok, see my update.
    – bstpierre
    Dec 17, 2012 at 16:20
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Try the speakers with another device, MP3 player and so on. If it works, then installing a sound card in your computer and disabling the integrated sound card will fix your issue.

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"Sounds like" there was a short or something because of that bump and you probably have a damaged audio chip now.

To rule out the software part, first try to boot off some other live linux distro and check if you still hear the hiss.

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  • It does not appear to be software, I booted into a different partition and the hiss was still there.
    – bstpierre
    Dec 26, 2012 at 14:17

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