Not sure. Do this - Go to Settings, accessibility and scroll down to Notification Reminder and see if that is turned on. This plays a notification reminder for any selected app every two minutes. Not sure if this would be teh problem, since you don't show any notifications. If it is, you can check to see which app is enabled to remind you or turn it off completely.
Not sure what else would be causing it, but I'd shut your phone down, then once powered down hold the Vol Up button, the Bixby button and the Power button all at the same time until you see a Droid appear. You will then get a Droid mascot with a message about command not found. Wait a minute more and you will get a menu that will pop up. Use the volume down button to scroll down to the option to Wipe Cache Partition (be careful you don't choose the one below it to Wipe/Reset the Device). Use the Power button to choose the option and it will wipe the cache partition then give you an option to Reboot the device.