I have exactly the same problem with a REPLACEMENT PIXEL I received four days ago. I notified Google, then had a Tech evaluate. The microphone is a motherboard problem, apparently. I have tried every Google solution, including running phone in Safe Mode, turning off Blue Tooth, rebooting, etc. I am returning this replacement to Verizon today and asking for a loaner phone. Another option? Xfinity has mobile service for $45.00 a line. That's half of what I am paying Verizon for a broken replacement phone . . .