Google says Pixel audio issue is a hardware problem
Google offered a full refund to Buckman, basically admitting that this was not a problem that could be repaired via a software update. And that was confirmed by a new email from Google dated January 13th, which states that the problem is a hardware issue and that no refunds are being given out at this time. Instead, the company is offering a warranty replacement to affected owners of the two devices.
Buckman did come up with a workaround that will take care of the issue if you are experienced with flashing custom ROMs on your phone. This manages to eliminate the static distortion that is annoying Pixel and Pixel XL owners.
Now that Google has confirmed that the problem is hardware related, your best bet is to put a claim in for the warranty replacement. Otherwise, you will have to live with the distorted audio.