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?
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.
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.
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.
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).