one of my male honduran redpoints seems to have gotten an attitude towards one of the pimelodus pictus cats, i was sitting in front of the tank when he went for him and heard a low grunting sound is this from the catfish?
There are catfish that do make noise. A guy I work with said channel catfish will make a really weird sound when you pull it from the water. There's also a species thats labeled as a "talking catfish"
Different kinds of fish will croak, grunt, squeak, chirp or 'bubble' if they're aggrovated, excited, etc (seems like fish are the most vocal when breeding and eating =P)
What sounds like grunting from a catfish is usually something called "stridulation", or at least I think the term is correct. It is made by the a bony spur on the pectoral fin "spines" rubbing against another bone. Usually made when they are fearing predation.
It can sound like clicking, croaking, grunting, or a sound not unlike a pig.
My school did an experiment with juvenille channel catfish and largemouth bass. Stridulation observed when largemouth bass were feeding.
And yes, a smaller channel cat will totally do this to you when you are holding them pulling a hook out. You can usually see or feel their pectoral spines lock perpendicular or alternate in and out in order to make the noise.
My mom had a largish albino cat of some sort when I was a kid... It jumped the tank a few times and we always knew the moment it happened because the fish screamed like a woman. Freaky in the middle of the night.