Pixel 4a makes a mystery sound with no notification
Note: This is similar to https://android.stackexchange.com/questions/171359/mystery-notification-sound , but not the same symptoms, so I believe it is a different thing.
For about the past month, my phone has made a mystery sound almost every day. Video of it occurring here: https://youtu.be/cP4fYYouaAg . It typically happens some time after 9am, and it comes with no notification. As far as I can tell, there's no visual indication of what's happening at all. Does anyone know what this sound is??
Google Pixel 4a on Mint Mobile. Formerly T-Mobile prepaid.
Things I've tried
- searched through all of the phone's built-in notification sounds. This isn't one of them(!)
- turned off NFC, still happens.
- turned off bluetooth, still happens.
- noted location that it happens, doesn't matter (not consistent). Note that when I say location, I mean both geographic location and the phone's proximity to other devices (neither seem to matter).
- noted times of occurrences. Not consistent. Doesn't happen every day, but on the days it does occur, it's usually between 9am and 9:30am CST.
- I wrote down the exact second that this happened one day, then searched the phone's developer logs from adb logcat -b all. There were a handful of entries in the seconds surrounding the event, but all of those entries are common occurrences throughout the logs, so they can't be associated with this. In short: this sound leaves no trace in the phone's internal logs.
Thanks in advance for any suggestions!
Following a suggestion from a user on a different forum, I put the phone into safe mode for a few days. This deactivates all external apps. (In the power menu, long-press the power off option.) While in safe mode, the phone never made the sound, which proves that it is some external app.
I am currently in the process of uninstalling my external apps, starting from the most recent. Each day, if the phone still makes the noise, I uninstall the next one. I am bound to find the offending app eventually. (Note: yesterday, I uninstalled Duolingo and it didn't make the noise today, so this may well be it. Couple more days to be sure...)
Final thought: why would an app do this? Though I have no direct evidence of this yet, I suspect that an external app was giving me a lot of notifications, so I must have long-pressed one of those to silence that app's notifications, but somehow, the sound is still getting through. Perhaps a bug is present in that app.
Thanks for suggestions above!