Happened to my pixel xl after a very minor fall. Turned out that one of the T5 torx screws that secures the display cable bracket (1:54 in ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Rau-vTrMgdo.html) was missing.
Pinch the screen where your selfie camera is at as hard as you can. No, this is not a joke. Its where the connector for your screen is under the glass...
I have the same issue happening with my Pixel C. Will the same thing work? James did that fix it for you? I'm assuming it did given you hearted the reply
Uhhhh. You'll want to get that checked. the sound going out is the first indicator of the battery going bad in my experience. The battery bulging lifts the contacts for the sound out of place and stops the speaker working.