Pattern visible with carpaint material

[paulmelis]

I'm seeing a sampling artifact (my guess) when using the car paint material. Here's a crop from a render (you might need to zoom in to see it better):

The pattern appears irrespective of the viewpoint being rendered from. When replacing the car paint with a metallic paint material the pattern is gone, so it appears to be the car paint shader (I also don't see it anywhere else in the scene):

Not sure how relevant this is but the settings on the car paint material are: