Hi @zelec ,
I don't know but the audio codec chip contains a digital to analogue decoder for the received digital audio to operate the analogue receiver/speaker in the phone and the microphone needs an analogue to digital encoder so that the voice transmission can be sent digitally, presumably they both could be contained in the same chip.
Have you tried starting the phone in [https://support.google.com/pixelphone/answer/2852139?hl=en|safe mode] to see if the problem occurs?
Have you tried a factory restore to see if this resolves the problem?
Just some thoughts.