There are two minor Easter eggs on this map.
In the Help Room, to the right of the Mystery Box lies a radio. When that radio is stabbed or shot, it will play music. Doing so again, will cause the song to change.
In World at War, it will play various songs including the Black Cats soundtrack, the Red Army theme, the Königgrätzer Marsch or WTF.
In Black Ops, it will play many of the same songs from World at War along with new ones.
In Black Ops III, it will play a variety of songs used throughout the Zombies game mode
The song "Undone" by Kevin Sherwood can be activated when you shoot three Explosive Barrels around the map. You do not need to make them explode, just shoot them once to trigger the song.
All three barrels are visible from barriers in the starting room. This can only be done on the Black Ops and Black Ops III versions of Nacht der Untoten.