What causes strange interference when connecting a second monitor?

Question

Iron

Intel hd graphics 4000 video card, gigabyte ga-b75m-d3h motherboard.
With 1 monitor everything works fine.
Now 2 LCD monitors with different resolutions are connected in desktop extension mode. Periodically, the image on one of the monitors (on an arbitrary one, no regularity was noticed) "collapses" sideways (usually to the left) and is restored on the other side. Those. visually, if you do not look closely, it looks like a black bar running across the screen. This happens very quickly, video recording will not work. Strongly resembles problems with a scan on a CRT TV, but 0_o.
The frequency of such interference depends to some extent on the processor load, but is not determined by it. If the computer is not in use, they appear every 5-10 minutes, if something is hanging in the background that is eating a lot of the processor and / or video card, the interval between them is reduced to 1-2 minutes. No connection was found with dragging windows, filling the monitor with some color, launching applications, connecting USB devices.
1 monitor is connected via HDMI, the second - using VGA. The problem manifests itself in the same way. Monitor manufacturers are different. The frequency is set to 60 Hz.
AtiTool in artifact search mode does not react in any way.
What could be the problem?
(please do not send me to Google, and also do not advise me to buy a new monitor / cable / video card. For googling gave me only answers like "buy d - get d", which infuriates me inexpressibly.)

Answer 1

Are the problems identical for both types of connections? Most likely a hardware problem.
I would go in this order:
1) Update drivers
2) Update BIOS
3) Try another processor
4) Try another motherboard
Items 3 and 4 can be swapped if desired. Before that, for fun, you can try another memory, but purely because it is easier to change.

Answer 2

With different resolution in extended desktop mode.

Try with the same resolution.