In the Daytime Spagonia stage (Rooftop Run) on both the PS3 and Xbox 360 versions of Sonic Unleashed, in the middle of one of the curves, a pedestrian will be reading a newspaper. Upon further inspection, there is a, albeit blurred, picture of the box art for Sonic the Hedgehog (2006) to the upper right of the paper.

In the Xbox 360 release of the game, you can turn off a stage's music by playing personal music via the Xbox Guide and then pausing it, allowing for harder-to-hear ambient/field recordings that play in the background of certain stages to be heard. For instance, one spot in the Nighttime Spagonia hub area plays a sound clip of someone whistling while taking a shower; the song being whistled is Sonic Unleashed’s theme song "The World Adventure", and a shortened edit of the same whistling is featured in the first teaser trailer for the game.

The music track "Rooftop Run (Night)" in Sonic Unleashed contains a well-known and common jazz lick (1–2–♭3–4–2–♭7–1) which would go viral and become known as "The Lick" in 2011, three years after Sonic Unleashed's release.