Plutonium

so. in die rise when you play as stuhlinger, you can hear him hallucinate zombie groans (because he has been exposed to element 115 via eating zombie flesh)
one thing i've noticed about this is that it persists into other maps, this scared the shit out of me exactly 10 minutes ago while i was playing buried as misty.
is this a plutonium exclusive issue or does this also happen on other versions of the game?? im asking because i cant find it documented anywhere.