Try changing your equalizer settings. No such problem for me. Or, use an app like Kernel Adiutor to up the volume.
Disable camera app, Google "Pixel camera.apk", download, install, profit. You can do the same with Google assistant, uninstall Google app, Google "Google assistant", you should be able to find a page quickly that has like three files for download. You flash two of them, profit. I didn't have to do this to get it working, but it should fix it for you. Or you can try clearing the data/cache of the Google app, maybe uninstall the updates and reboot.
Pixelicious 7.1.1, Pixelized 7.1.1, Pixel Envy 7.1.1, Pixel for Nexus 7.1.1, a few ideas. I'd it were my build, I'd go with Pixelized.