WiFi causing screen flickering. Is it possible?

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I’m a bit baffled.

I’ve a Lenovo Thinkpad X1 Carbon 8th gen.
I’ve used it with Fedora Linux 34 and 35, and now I’m using Fedora Silverblue 35.
It has always worked very well.

Usually I use it connected to the Ethernet.
In the last days (vacation time!) I’ve mainly used it using a WiFi connection.

In the last days I noticed an annoying problem with the display. Artifacts, glitches, flickering, sorry I don’t know the right term. I can’t take a video, I can only upload some pics hoping that they give you an idea (please imagine them in motion).

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I was already in despair :pensive: because I booted with a live Fedora Workstation 35 (thus an older kernel and so on), and the problem was here as well. Ouch, an hardware problem. But oddly, no problem accessing the BIOS, running the health checks, or while on GRUB and on LUKS password spoke. :thinking:

I observed that such annoying behavior was particularly noticeable using Firefox. The issue was additionally evident watching some online videos. Maybe something related to the browser? (Hardware acceleration and so on). No. Same issue with Chrome.
The display became practically unusable downloading an ISO using curl. Yeah, these glitches/artifacts/flickers seemed to be increasing with an increased network activity.
So I had an idea. The WiFi access point is dual band. I was connected using 2.4 GHz. Mmmh, let’s try to connect to 5 GHz. And you know what? The issue has gone. :open_mouth:

I then reconnected using the 2.4 GHz frequency band various times, to make a countercheck. And ta-da! the display problem has reappeared. Switched back to 5 GHz, the problem has gone.

Well. The question is: is it possible? Is it scientifically possible? :sweat_smile: How could WiFi frequency interfere in that way with the display? Should I expect that the problem is not that and the laptop actually has an hardware issue?

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You did not say anything about the GPU or driver.
You also did not say whether this occurs when using wayland or X.
Which DE? gnome, kde, xfce, or ?

Usually the first place to start looking when video issues appear is the GPU driver in use and the display manager and DE.

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@computersavvy I said it: I’m baffled. The issue does not show up connecting to the 5 GHz WiFi frequency (or turning off the WiFi, of course).

Xorg or Wayland doesn’t make any difference.
As said, the DE is GNOME.
For what it worth the kernel is 5.15.12-200, but also with a live Fedora Workstation 35 (what kernel was shipped at that time? 5.14?) doesn’t make any difference.

About the graphic card:

00:02.0 VGA compatible controller: Intel Corporation CometLake-U GT2 [UHD Graphics] (rev 02)
	Subsystem: Lenovo Device 22be
	Kernel driver in use: i915
	Kernel modules: i915
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From your very complete description it seems that the use of the lower freq wifi may indeed be causing the issue. I would suspect there may be a loose or deteriorating connection with the wifi card or its antenna that is causing static that interferes with the video. It also may be a connection to the video that is deteriorating. The only way to check that and clean/reseat the connections is to open the laptop so you have access to the motherboard and attached components.

If you do not feel comfortable doing that yourself there are places you can have it serviced (for a price).

It is not difficult and there is likely a ‘how to’ on that subject for your laptop that can be found online.

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Yes it possible. In my experiences (maybe not related with your case) there also possibility with bad grounding.

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