Why is Metroid Prime 2's subtitle Echoes?

[RedLink]

This is just something I've always wondered. MP3 Corruption makes sense since the Phazon is infecting Samus's suit, but why is MP2 called Echoes? Is it a reference to the dark aether being an "echo" of light aether?

What're your thoughts?

 

[SavageWizzrobe]

It probably refers to Dark Aether being an "echo" of Aether. Another possible reason is that there are some sonic puzzles and items in the game; if not for this, the subtitle could have easily been "Darkness" or "Shadows" or something like that. Plus, "Echoes" has a nice ring to it.

 

[Jirohnagi]

As Savage said it is because Dark Aether and it's inhabitants are mere echos of the real Aether heck even Dark Samus is just an Echo.
Plus i think the Echo puzzles were squezzed in cuz they don't seem to fit