Environmental Sound (Silence 2) (環境音（静寂2）) is an ambient theme in Metroid Fusion. It is a slow, quiet theme with a piano melody and another "screeching" instrument that is also heard in the Ending theme.
This theme plays at various points in the game: during the cutscene where the "Federation official" asks the ship's computer if Samus suspects anything, and as Samus is taking a detour to her Gunship during a power outage caused by vegetation. The theme continues playing as she encounters Ridley's frozen corpse in the Sub-Zero Containment room, which can be entered from the other side early in the game; this theme will play in that instance as well. It is last heard after Samus escapes the imploding Restricted Laboratory and communicates with her irate computer, who reveals that there are ten SA-X aboard the BSL Station.
The theme can be heard here.