Check if the issue occurs during calls or when using third-party apps such as Skype or Facebook.
1. If the issue occurs in third party Apps. It is recommended to back up all the data and reinstall the third party Apps.
2. If the issue occurs only in calls, check if the issue occurs in every call.
3. Open the voice recorder or any third party voice recorder App, and record a short audio. If you hear a recording and the sound is normal, please try calling from a different location with a good network.
4. Restart the device to check if the issue persists.