It seems as though a handful of people are experiencing severe problems with their microphones on their Pixel and Pixel XL devices, as evidenced by this thread on the Google Product Forums. The poster describes the issue as persisting through a factory reset of the phone, though it doesn’t seem to affect the camera app.
Received my pixel today and after a few hours of use and set up the microphone stopped working entirely, except when recording video upon which it’ll record audio fine as if nothing were wrong. I factory reset the phone and the issue still persists everywhere but the camera app.
Google has acknowledged that this is specifically a hardware issue and not a software issue, so it can’t be fixed through software updates. The rep further mentions that they’re going through a more rigorous process when certifying refurbished phones to make sure they don’t have this mic defect.
The rep says they’ve also taken steps to reinforce the mic connection during manufacture so this issue won’t pop up. Phones that have been built in the last month should not exhibit the mic problem. If you do have issues with your mic cutting in and out or it stops working all together, Google recommends you seek an RMA on the device or contact the retailer where you purchased it.
[via Google Product Forums]