In Accelerando, there was a similar plot device. The anisotropies in the CMB (or maybe just minor aberrations) were caused by waste heat from Type IV/V civilizations running gigantic computations (trying to probe/find vulns in the laws of physics, if I remember correctly).

I thought that was a cool idea: that something as studied, ubiquitous and generally accepted as a natural phenomenon as the CMB is just a landfill, we just don't know what we're looking at.