Hi @Mhaku, welcome to our forum and I'm sorry to hear about this.
To start with, could you please get back to me with which phone model and Android version that you have? This will help me troubleshoot the behaviour in the best possible way. You can find this information in Settings > About phone.
If you are using a case on your phone where you have a credit card and/or bus card, try turning off the NFC function in your phone and see if you still hear the sound. You can turn NFC off in Settings > More > NFC.
If there is no change when NFC has been turned off, try rebooting your phone in safe mode so we can see if one of your downloaded applications is the cause of you hearing this sound when you can't see a notification as they will be temporarily disabled while the phone is rebooted in safe mode.
Let me know how it goes!
