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Several times in a day, my desktop sometimes is corrupted by black noise with a particular pattern (it's not "white noise"). My CPU has integrated video, so I assume it borrows memory from the system. My two monitors have VGA and HDMI interfaces and it happens to both. What does this noise suggest, corrupt memory?

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What about the cables? Are they digital or analog cables? Are you connecting digital to digital and analog to analog? Do the cables have ferrite rings on them? Are they plugged in securely? Do you see more/moving noise when jiggling the cables? –  Synetech Oct 5 '12 at 21:55
    
VGA is an analog standard while HDMI is digital. The cables are fine. –  Emre Oct 5 '12 at 22:00
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This definitely a possibility but usually when you have bad memory you will have other issues with your system (like it not booting). The closest scenario I have experienced similar to yours was when installing more memory in a desktop PC, noise was present in the display during POST in the form of random characters and patterns. The system would hang upon loading the operating system and changing the faulty DIMM fixed the issue. With RAM prices so low nowadays it might be worth is to install new RAM and see if it resolves your issue.

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You are very close. I did install additional RAM and it did fail to POST. I removed one of the two additional sticks to see what would happen and it sort of works but I get the aforementioned noise. This is in fact a replacement pair of memories so I'm not sure I want to get a third pair before being sure. –  Emre Oct 5 '12 at 1:36
    
If you have a graphics card lying around that is compatible with your motherboard you could try that as well. When you say additional RAM, try using only one stick total (of the new batch). I've also seen nose in the form of vertical/diagonal/horizontal lines that are output from onboard VGA. –  Mike Oct 5 '12 at 1:40
    
Yes, in bands along the axes. Unfortunately I don't have an extra card. I'll try different memory/slot combinations and see what happens. –  Emre Oct 5 '12 at 2:51
    
Don't bother with the RAM. From what you are describing it sounds more like using a dedicated card is your solution. –  Mike Oct 5 '12 at 3:16
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Gwt an anti-static wrist band. Put your finger on the chips and see if you can feel vibration from the noise. You can also use your ear, try to figure out where the noise is coming from. Obviously remove any unnecessary cards. Try to figure out how to predict or trigger the noise. If you can trigger it or predict it you can more easily find the source. See if the noise occurs even when the computer is in the BIOS, then you know it's not software doing it.

Once you isolate more where the noise is coming from e.g. a particular chip, then you could google that see if others have the issue, you can describe it here.

ADDED

The questioner clarifies that he meant video noise not audio noise.

I mention, possibility of using a cheap video card to troubleshoot, and if that works(no video noise), then you could use that card, or get a pricier video card. Or you could replace the motherboard.

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This is a horrible suggestion and guaranteed will fry something if done wrong. Based on the author's technical expertise its likely this is exactly what will happen. –  Ramhound Oct 5 '12 at 11:19
    
Why don't you tell us what would go wrong. If he follows as suggested then fine. I suppose in a worst case scenario, if he doesn't use the anti-static wrist band correctly, and he is very unlucky, then his computer might break if he touches a chip, but I seriously doubt that even that would happen. I've had no problem doing that on old computers of mine with no anti-static wrist band. Similarly, there is no risk of electric shock either. You seem to be spreading FUD. Why don't you say what you think would go wrong? This is a technical forum and I don't believe in hiding solutions. –  barlop Oct 5 '12 at 13:15
    
I do use an anti-static wrist band, but I should point out that I'm not referring to audio noise, but visual noise. How will my ears help? –  Emre Oct 5 '12 at 19:14
    
@Emre oh, I thought you meant audio noise. You can get a video card very very cheaply on ebay, (I use a few for troubleshooting, it cost me like a lot less than <$20 perhaps), plug it in and see if you still get the problem. If it works fine with a video card, then i'd think it's the motherboard. May well be video ram chips on there, but i don't think you can do anything about that, can't replace them so nobody really looks into troubleshooting them, they'd just replace the motherboard or leave the motherboard. You could then get a pricier video card if you don't want a cheap one. –  barlop Oct 5 '12 at 21:47
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If I'm understanding you, it sounds like a software problem. It sounds like you're saying that pixels and maybe small blocks of the screen go black at times, until refreshed somehow. This is usually an indication that the "bit-blit" algorithm used for doing graphics was not too carefully implemented. (Yeah, I know that bit-blit itself is now rarely used, but the general category of algorithms remain.)

Basically, when, eg, moving a mouse across a screen, one needs to quickly compute the changed image as the mouse moves over an area of the screen, and then just as quickly restore the original data after the mouse passes. This usually works fine, but if something else is going on at the same time (eg, another image pops up on the screen where the mouse is moving) the wrong data may get processed.

The likelihood of this problem occurring depends on how much is going on, how overloaded the box is, the quality of the display graphics code, and the hardware display controller.

On the other hand, "streaks" of black pixels that sort of dance across the screen would be due to some activity that is holding off access to display memory. In schemes involving shared display/RAM memory this could be disk I/O (which necessarily needs highest priority RAM access).

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The pattern does not move that much and it disappears after a second. I stress that I am using an integrated graphics unit so the memory is probably borrowed from the system. –  Emre Oct 5 '12 at 22:30
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