The Google Pixel 3 and 3 XL were plagued by a lot of issues initially but many were already addressed via software updates. One of those that remained was the poor audio quality while recording videos.
Google Pixel 3 and 3 XL get an audio fix when recording video
Luckily, there's a patch that aims to fix that and it's already seeding. It's part of the latest update that Google delivered to its flagship duo.