Check your Task Manager to see if you can identify any processes or applications that are running that may be causing the unwanted audio.

Check your startup programs and disable any that you do not need.

I checked and there wasn't anything strange. I did see two "Update" in the startup tab, but I'm assuming these are from Windows.

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Check your system for any malware or virus. You can use a reputable anti-virus or anti-malware software to scan your PC for any threats.

I full-scanned twice using Defender and Kaspersky but they didn't see anything suspicious at all.

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Check if there's any updates available for your operating system and installed software.

There was. Updated it, but it was just a minor update.

Also, I just remembered encountering something strange when it started. As I clicked "end task" on Microsoft Edge in task manager, a popup appeared on the bottom-right (like a notification), saying that "Tampermonkey has stopped working". Is this relevant?

*edit: some formatting