Yes, UbreakIFix performs in warranty and out of warranty repairs on Pixels. The issue you described with the audio IC chip is an issue that is covered even if you are out of warranty. We typically perform a motherboard swap in cases of audio IC issues at no cost to the customer.
I don't see any reason why they would not help with the fix (especially if Google recommended you go to them). I had them replace a screen that was causing the phone to constantly reboot and they did a great job. Also, just as an FYI, some of the early pixel 1 models had a bad cold solder joint on the mic which caused similar issues to what you are referencing. Hopefully it's not that but don't be surprised if it is.
Thanks! Your answer is awaiting moderation.