Speaker noise when metal USB plug touches my computer case and other electrical problems.

November 1, 2009 4:21 PM

Speaker noise when metal USB plug touches my computer case and other electrical problems.

I have an aluminum PC case. Whenever the metal USB plug from my external drive contacts the front, I get crackling from my speakers, which are connected to an external USB soundcard. (This crackling happens even if they're not connected to the actual output jack.) A few possibly related problems: my audio occasionally starts popping once every few minutes, and my USB devices sometimes play the "connected" sound in Windows even though they're already connected, as if they're briefly disconnecting.

My guess is that this has to do with the grounding, but I'm not sure exactly what to do. My case has a round grounding wire, but I don't know where to attach it, and fiddling with it didn't seem to have any effect. Suggestions?

posted by archagon to computers & internet (8 comments total)

The grounding wire on your case - is it coming from your powersupply? You can attach it anywhere on a metal part of your case, normally though, the metal case of the powersupply is grounded, and since it's screwed into the metal computer case with metal screws, the case is automagically grounded too.

Sorry, I don't have many ideas for your USB problems. Is your computer connected via a power bar or UPS which may have a broken ground connection?
posted by defcom1 at 4:46 PM on November 1

Could you be more specific when you say "My case has a round grounding wire" ?

Assuming you're in the U.S., your computer should have this kind of plug. The ground wire is the round one. Attaching it shouldn't be optional. It should go in a grounded outlet. You can check that your outlet is grounded by plugging in one of these and examining the lights.

If your outlet is not grounded move your computer to an outlet that is grounded, and only use that outlet for appliances with two plugs instead of three.
posted by odinsdream at 4:52 PM on November 1

is it from the case itself, or the power supply? the metal case on the PSU is usually grounded; you can attach it to the power supply (not sure how without seeing what you have, though).

also seconding odinsdream and adding that if you're using a 3-prong converter deal, you must have the thing screwed in and the outlet/box must be wired up to support that - meaning the junction box the outlet is attached to needs to be grounded, or there needs to be a ground wire in there attached to the plug's frame in some manner. you can check this with a continuity tester or an outlet tester; some power strips have a "ground fault" light that will tell you if the outlet is wired properly. if you don't have this, you're not grounding your computer and bad things could happen.
posted by mrg at 5:39 PM on November 1

The grounding wire is attached to the front panel of my case and ends with a small, metallic loop. This has nothing to do with the power supply.
posted by archagon at 6:29 PM on November 1

Does your plug have three pins? This is the proper method of grounding, not a loose wire that you're expected to fiddle with.
posted by odinsdream at 7:11 PM on November 1

archagon, is there a metal segment on the front panel of the case which isn't touching metal on the rest of the case? (As in, it's surrounded by plastic.) If so, is one end of the grounding wire attached to this metal segment?

If this is the case, I'm fairly certain that you're supposed to attach the loop end to a screw touching metal in the main part of the case so you ground the front panel, too. I really can't say if this will fix your speaker problem, though.

Otherwise, you need to be a bit clearer as to what this grounding wire attaches to, exactly. This isn't a common feature in computer cases, so that's where the confusion comes from.
posted by wsp at 8:28 PM on November 1

Yes, my PSU has 3 prongs.

I think you're right, wsp: the grounding wire attaches to the front USB ports and audio jacks, which are surrounded by plastic and separated from the rest of the case. Most of my electrical problems come from those jacks. I'll try to attach the loop to a screw.
posted by archagon at 9:02 PM on November 1

It is probably grounding issues. But your random USB connect sounds make it sound like you may have a flaky USB setup. There is also the possibility that you need to put chokes on your USB chords.
posted by chairface at 10:50 PM on November 2