Please follow methods below for troubleshooting:
- Increase volume in Settings > Sound > Volumes > Music, video, games, & other media.
- Increase volume in the settings of apps that play music or video files.
- Play another music file with the same app to test.
- Play the same music file with another app to test.
- Update firmware to latest version: Go to Settings > About > System update > Check Update.
- Access Safe Mode by long pressing power key > tapping and holding Power Off > tapping OK. If your phone works well in Safe Mode, there may be some 3rd apps that cause malfunction. Please reboot your phone and check again if it works well.
- Backup your data and perform factory data reset.