Noise during videos and poor call quality

Hello!

My iPhone started to record 95% hissing noise during videos (rear-camera is the worst, but front-facing video is only slight better), you can only hear the real sounds in the video very little. The only sound that is pretty much ok is the voice messages and audio recording, for example in whatsapp and viber everything is about ok.

Normal phone calls are also bad quality, i basically have to speak very clearly and the other person might hear my words only partly and the dB of my voice changes dramatically.

What parts do I have to change? I've reseted my phone numerous times and phone is currently running 11.2.5 but i think that these problems came before ios11.