Microphone doesn't work for few seconds on iPhone 7

Hi!

I've got a problem. My microphone doesn't work for about first 2 seconds while recording on front camera. Same goes on Messenger but on both cameras (and for first 4 seconds). You can hear a quiet noise at the beginning, and after that microphone starts catching the sound properly. This results in not working Siri (she can't catch the first words I say) and Hey Siri (I even can't launch "Hey Siri" in the settings because it entirely doesn't catch my voice or any sounds).

I've already restored my iPhone, updated to the newest version, took off my case and nothing works.