@beccatha: Can you confirm the model number and current Android version of the phone, located in Settings > About Phone? Next time you hear the beeping sound, try heading to Settings > Notifications > Recently Sent, to see if any apps are listed that correspond time wise. It may be an app working in the background, such as an email app, so it's worth exploring as a possibility.
Hi, I had the same problem. I tried all things that often mentioned in the beeping problem:
1. Nfc. Not worked, mine doesn't have one
2. Check notification log. Also nope, no app detected
3. Turn off notification reminder. Nope
4. Sim card setting. Nope.
5. Disable developer option. Nope.
6. Reset app preferences. Yass worked! But only for couple days, aaand you have to set the apps setting again. Meh.
7. This is what worked for me: Setting->Apps->Permission Manager->Microphone->GOOGLE->change the allow all the time to deny. But this might affect the google assistance or something.
And then I remember that the beeping sound was started since I installed google assistance. So maybe evaluating the apps that you installed and set the setting will help to stop the random beep.
My device: Samsung A20s, Android 11.