It seems that following the iOS 11.3 update, some iPhone 7 and 7 Plus owners are reporting issues with their microphones. According to the reports, some users are claiming that they can’ be heard during phone calls or FaceTime video calls. The good news is that Apple is aware of the problem and plan to address it.
According to an internal document distributed to Apple Authorized Service Providers obtained by MacRumors, Apple has acknowledged the issue and have informed these service providers of the problems that they might be hearing from customers. It doesn’t seem to be a particularly widespread problem but it does sound annoying enough.
Unfortunately it also doesn’t seem like a problem that can be fixed with a software update. According to the document, Apple is prepared for service providers to initiate a repair for the iPhone, meaning that they believe that this could be a hardware problem. Apple also seems to be allowing service providers to make an exception for iPhone 7 and 7 Plus handsets that are no longer covered by warranty, meaning that you could probably get it fixed for free.
In any case if you are experiencing issues with your handset’s microphone following the iOS 11.3 update, you should probably make an appointment with an Apple Authorized Service Provider to get it looked it.