What is causing this digital watch-esque beeping noise sometimes?

I generally leave my computer suspended overnight; in the morning, when I wake it up, I will occasionally be greeted with this awful beeping sound. The sound is like this - https://gitlab.freedesktop.org/xdg/xdg-sound-theme/blob/master/stereo/alarm-clock-elapsed.oga

Usually, it is 5 pairs of beeps. This morning, only 3. For the longest time I have thought it was a hardware issue or coming from the motherboard. But it occurs while the computer is on and running fine.

I cannot for the life of me figure out what is going on here. I've seen this issue, which feels close to correct - https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/652

But even without an upcoming calendar event, I still hear the beeping. It is only right after waking the computer up from sleep. Has anyone else dealt with this?