He's not eating well, and in fact not at all. But I've only had him three weeks, and it is winter and he's a year and a half old male...
So, I think I may have gotten panicky for nothing, I haven't heard another single noise out of him, not even when I had to pick him up today to clean his tank again. The little brat upended his water dish and somehow got all (I mean in it's entirety...) of his substrate balled up inside it. I'm not even mad, I'm impressed.
I'm still going to watch him closely and listen for any other noises, though.