Chosen Solution
Ok so I have a weird issue with my IPhone 7plus, whenever I record with my back camera, there’s sometimes no or very faint audio. But then later in the video the audio is fine?? And sometimes it’ll switch between the two on one video.
The iPhone 7 model is prone to audio problems. It could be due to a faulty part or worse the audio IC chip. I suspect your problems are due to a faulty mic on the dock flex assembly. There are two microphones on this component and if one has become faulty it would produce the symptoms you are experiencing. Replace the dock assembly from a reputable supplier and it should be fine.
