I was browsing the intel of the campaign and... wtf, in the project nova (If I remember well) intel was written something about the wunderwaffe program, and that an (I don't remember  :roll: ) gave them a machine capable of time travel! 
Now watch the NDT loading screen and...! 
So I thought a theory that explain that: 
Silence and zzzzzzzzzzzzzz can mean that they are sleeping=they are dead, so a survivor went into a american storage and used the teleporter to go to NDT, to prevent the 115 infection with the three tests subjects that survived the 115 exposure. 
What do you think? 
P.s: Sorry for my bad English.