Apple acknowledged that some iPhone 7 and iPhone 7 Plus had a sound error when calling

An internal document sent by Apple to Apple Authorized Service Providers this week revealed that users can see the speaker icon while calling or video call through FaceTime faded, and make them talk but the other party cannot listen. Users have complained about this error on Reddit and Twitter the past few months.

Apple has recommended service providers to guide customers on their own by disconnecting or disabling Bluetooth headsets or other audio-enabled devices connecting to the iPhone. If the speaker icon is still grayed out, the technical support will perform audio testing. If the device has a 'device could not detect dock' or 'accessory not supported' message, the support will start to fix the error.

Some iPhone 7 and iPhone 7 Plus machines running iOS 11.3 or higher have a sound error

Apple does not state whether the repair is free but if the warranty expires, Apple will still require an exception for these cases. Although not a widespread problem, there have been many complaints about iOS 11.3 users' microphone in the past few months.

See more:

1. Apple released iOS 11.3.1 update, fixed the touch error when the iPhone replaced the screen not genuine
2. Fix battery drain on iPhone when updating to iOS 11.3
3. Common errors after iOS 11.3 update