I think this may be a Linux thing, not Zorin-specific, as I just had the same annoyance while trying a Fedora KDE 44 live session.
Fairly regularly I get a biddle-ee upward sound (like an "opening" notification), followed a few seconds later by a biddle-oh downward sound (like a "closing" notification). The taskbar blinks momentarily, and if I have a menu open (like the Zorin taskbar menu) it disappears as if the screen has been refreshed.
Does anyone recognise this behaviour? I'd be very grateful for any hints.
That sounds for me like something gets plugged and unplugged. Did You checked if Stuff like Keyboard, Mouse and other USB Stuff in plugged in correctly and complete?
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Do you have bluetooth devices which connect / disconnect? Maybe something fails to connect correctly.
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I did consider that, but the only USB device capable of interaction is my wireless mouse, and I've left that switched off and unused for weeks, but this occasional flickering still occurs. Baffling... 
And my Bluetooth is also switched off.
for the record since gnome 46, Canonical's geniuses removed any notification for bluetooth or USB (did I said geniuses?!), that's why I rebuilt some for my computer...
So it can't be that, maybe charger
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Not the charger either. It's unplugged. I went through every notification in Settings and switched them all off, and still the flickering continues. Annoying and baffling... 
if its flickering, did you try to press all around your screen to see if the internal Displayport is not damaged ?
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"Flickering" is maybe the wrong word. It's a tiny very brief one-time refresh of the taskbar which simultaneously clears any menu coming off the taskbar - the Zorin menu on the left or the status menu on the right. Now that I've switched the sound off, even though the refresh is annoying it's not a deal breaker - I can live with it. At least it's not Windows, right? 
Oh, and to better answer your suggestion, it happens on both my laptops, one of them brand new. I'm 99.999% sure it's a Linux software sound.
didi you try to disable all gnome extensions excepted taskbar to see if it could be that ?
launch a real time log to see what is wrong when it happen
tail -f /var/log/syslog
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When You don't use it, unplug it and check if the Behavior stops.
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Thanks for this suggestion. I ran it for 5 minutes with the Zorin menu open, and nothing happened. I rebooted, did the same again, and again nothing happened. Perhaps I've switched off the problem notification. I just asked the question originally because I thought it might be a known thing - apparently it isn't, and I guess I can live with it.
@Ponce-De-Leon - I haven't used the mouse on my other laptop for a couple of weeks, and the flicker happened on Zorin & Fedora.
No matter, people. I really appreciate the help and advice, as usual. Thank you all.
Does Your System run in Wayland or X11? You can check that with the Terminal Command echo $XDG_SESSION_TYPE
When it should show Wayland, try it with switching to X11/Xorg and see if it behaves different. To do that, go to the Login Screen. click on Your Profile so that the Password Field appears. When it is appeared, You should see a Gear Icon in the bottom right Corner. Click on it and choose the Option ''Zorin Desktop on Xorg'' and then log in.
Do You have Fractional Scaling in Settings>Displays active? Could You post Your Hardware Specs? I mean CPU, GPU, RAM etc. If You use Nvidia graphics: What Driver do You use.
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I'm on Wayland; if the problem reappears I'll try X11. No Nvidia; I have a Ryzen 9 with AMD graphics. Thanks again for your advice.
This continues to infuriate me, so I've been investigating more using Nourpon's syslog command (thank you again). This was the message provoking the notification:
"2026-04-22T08:40:44.284152+01:00 dah-ASUS gnome-shell[2410]: Failed to make thread 'KMS thread' realtime scheduled: GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: Name "org.freedesktop.RealtimeKit1" does not exist"
Further investigation pointed to rtkit.daemon, which also created the blinking notification, and I discovered that the two are related. One suggestion was to mask rtkit, which I did, but it didn't stop the blinking notification:
"2026-04-22T20:29:34.935553+01:00 dah-ASUS gnome-shell[2539]: Failed to make thread 'KMS thread' realtime scheduled: Failed to acquire RTKit D-Bus proxy: Error calling StartServiceByName for org.freedesktop.RealtimeKit1: Unit rtkit-daemon.service is masked.
2026-04-22T20:29:35.080639+01:00 dah-ASUS dbus-daemon[826]: [system] Activating via systemd: service name='org.freedesktop.RealtimeKit1' unit='rtkit-daemon.service' requested by ':1.75' (uid=1000 pid=2539 comm="/usr/bin/gnome-shell" label="unconfined")
2026-04-22T20:29:35.081366+01:00 dah-ASUS dbus-daemon[826]: [system] Activation via systemd failed for unit 'rtkit-daemon.service': Unit rtkit-daemon.service is masked."
If anyone can make sense of this and suggest a permanent fix I'd be very grateful.
Thanks, as always...
(Edit: Xorg session doesn't have this problem, but some websites don't work properly.)
Wayland enables the job, but only takes part of the load.
Whereas X11 does the job.
So, under Wayland, it is Gnome Shell that is calling the processes, and needs to request realtime priority to create a KMS (mode setting) thread.
It must request it because under Wayland, Gnome Shell is unprivileged.
Under Xorg, Gnome Shell is still unprivileged, but is not calling the processes, X-Server is. And it is privileged.
Masking rtkit will ensure that the log is generated since the Shell cannot access privileges.
So, you do not want it masked.
There are zero web standard services that depend on Wayland or Xorg. If some websites do not work on X11, which is mature and stable unlike Wayland, that is due to something other than the Display Protocol.
The notification sound and flicker:
This also does not seem likely to be caused by rtkit. That may be something noted in the log - but does not mean it is causing this issue.
In fact, it makes no sense that jounrald logs would get piped through notifications. I do not think there is anything in the code that could enable that.
BUT... if a DRM or KMS resets... Then Gnome Shell would need to request privileges again - and that would be logged.
It also could flicker the screen, close open menu dialog's and may make system sounds due to focus change.
What you see in the log is a symptom of that, not the cause.
You experienced this on KDE and on Gnome. Under Wayland, both act as compositors using DRM and KMS.
These are used by Intel, AMD and Nvidia.
So, really: DRM/KMS is what we need to look at.
Can you run
journalctl -f -o short-monotonic
And wait for a KMS reset, flicker, system sound thing... then note what is showing in the log?
Atomic Commit messages? Flip_done time out?
PSR exit?
KMS or DRM errors?
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Wow! You certainly know your stuff! Thank you so much. I'm heading to sleep, so I'll check out your advice tomorrow. Thank you.
Good morning, Aravisian.
Unbelievably, I'm unable to upload a txt or odg or odt document, so I'm forced to include just a relevant sample extract of the log. All of the events show the same thing at the point of notification - the rtkit event. I hope this will give you some hint. I saw yesterday a comment about amending a config file to change the rtkit reporting level - perhaps that's the avenue I'll follow, but I would still appreciate any advice you can offer. Thank you, as always.
========
dah@dah-ASUS:~$ journalctl -f -o short-monotonic
... (irrelevant stuff omitted for brevity)
[ 3132.044073] dah-ASUS CRON[69969]: pam_unix(cron:session): session opened for user root(uid=0) by root(uid=0)
[ 3132.066786] dah-ASUS CRON[69973]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
[ 3132.067066] dah-ASUS CRON[69969]: pam_unix(cron:session): session closed for user root
NOTIFICATION
[ 3142.546689] dah-ASUS rtkit-daemon[58714]: Successfully made thread 2572 of process 2539 owned by '1000' high priority at nice level 0.
[ 3142.547188] dah-ASUS rtkit-daemon[58714]: Supervising 1 threads of 1 processes of 1 users.
[ 3142.551376] dah-ASUS rtkit-daemon[58714]: Supervising 0 threads of 0 processes of 1 users.
[ 3142.552208] dah-ASUS rtkit-daemon[58714]: Supervising 0 threads of 0 processes of 1 users.
Well this all shows no failures of rtkit and it working correctly at that time...
Try:
journalctl -b | grep -iE "drm|i915|amdgpu|flip|atomic"
(I am not sure which GPU you are using...)
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Wow, don't you sleep...?
There too much info from that command to post here, but maybe this is the important line you're looking for:
Apr 23 08:22:57 dah-ASUS gnome-shell[2539]: DING: [000077c43cc16090] avcodec decoder: Using Mesa Gallium driver 26.0.4 for AMD Radeon 780M Graphics (radeonsi, phoenix, ACO, DRM 3.64, 6.17.0-22-generic) for hardware decoding
You can use pastebin.com if needed.
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