There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
Another fairly simple design drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Very simple, very blu(e). Subtle and nice.
Source Seb Jachec
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.
Source Atle Mo
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin