He's assuming it's not one of the skeletal crewmen they had since they weren't locked up last he heard.

"I did," Nihlus says when she mentions the sound, expression curious. "It seems to happen a lot just before I nod off. The hold's temperature is very comfortable for me and I, well, tend to get a bit drowsy during visits."

Come to think of it, Alice didn't see Shepard carry him out that one time, did she? Bit embarrassing, that.

Then she asks that question and Nihlus takes in a slow, deep breath.

"... The res attempts have not been successful with either Spearfall or Austen."