amitexe786 , via OnePlus 7T , Dec 26, 2020 : I have OnePlus 7T and I am also facing same issue. Randomly I hear one notification tone, when I unlock my phone there is no notification, really strange. Even I have reset my phone but still same mysterious tone. Secondly to find out more I have changed notification tone of other apps like sms, mail and other app to monitor which app has this tone sound. But this tone is something different.