Strange short sound on Windows 11 with no visible notification...

Artur, the file is a valid MP3, but I cannot confidently match it to a standard Windows sound. Since disabling the Windows sound scheme did not stop it, an application, service, driver utility, or hardware device is more likely.

Identify the audio session​

1. Press Win + R.
2. Enter sndvol and press Enter.
3. Leave the classic Volume Mixer open.
4. When the sound occurs, watch which green level meter moves.

Results:

• An application meter moves: that application generated it.
• Only the master meter moves: suspect a driver, exclusive-mode application, or hidden audio session.
• No meter moves: suspect the monitor, speakers, USB DAC, UPS, or another physical device producing its own sound.

A phone recording the mixer screen may help catch such a short event.

Capture file access with Process Monitor​

1. Download and run Microsoft Process Monitor as administrator.
2. Add filters for paths ending in .wav, .mp3, .ogg, and .flac.
3. Start capturing and leave it running.
4. Immediately after hearing the sound, stop capture.
5. Examine events from the preceding few seconds.

Process Monitor records real-time file, Registry, process, and thread activity. This can identify an application opening a sound file, although it will not catch tones embedded in memory or generated programmatically.

Perform a clean-boot binary search​

Do not merely exit tray applications; background services and scheduled tasks can remain active.

1. Run msconfig.
2. Open Services.
3. Select Hide all Microsoft services.
4. Click Disable all.
5. Disable startup applications through Task Manager.
6. Restart and test.
7. If the sound disappears, enable half the disabled items at a time until it returns.

Do not disable services before selecting “Hide all Microsoft services.” Return to Normal startup afterward to undo the test. Microsoft recommends this process for isolating background software conflicts.

Microsoft’s Autoruns can also expose non-Microsoft scheduled tasks, services, logon items, codecs, and drivers. Uncheck entries rather than deleting them so they can easily be restored.
My first test would be sndvol; it should quickly determine whether this is Windows audio or an external device sound.

have you got a pair of headphones connected by Usb, plug or Bluetooth?

Good point, ussnorway. Headsets can briefly disconnect/reconnect because of USB power management, a loose 3.5 mm plug, or Bluetooth interference, sometimes without displaying a notification.
Artur should test with all headphones/headsets completely disconnected or unpaired for a while. If the sound stops, reconnect one device at a time to identify whether the headset, USB dongle, Bluetooth connection, or audio-jack detection is responsible.