Koi Carp Fish Making Noises

[StaceFace]

I some how came about saving two fish after my ex boyfriend was about to throw them in the garbage because he didn't want them anymore, so I took them home. Well, after researching the fish appear to be koi carp, not too sure but that's what I've come to believe. I keep them in a tank, and they aren't that large, maybe a bit larger than goldfish. He said that he had them for three years and they never grew and I'm hoping they don't grow much. However, my one concern with them is that they seem to be making weird noises. It's hard to describe. Not sure if they ate aquarium rock because they are always picking them up and spitting them out. The sound is almost like a kissing noise but it sounds like gasping for
Air under water? Not sure! I only feed them once or twice a
Day at most. I do have a filter and they sometimes go to the surface to eat
The bubbles, if that makes sense? Please help!

 

[Lillefishy]

Koi carp are not aquarium fish, the reason they haven't grown much is because they're probably stunted having been kept in too small a tank.
Given the right conditions Koi can grow 3 feet or more, so need a large pond, they're also messy fish so need good filtration.
As for the noises it could be when there's food & they come up to eat they can make gulping noises.
I know you rescued them but tbh the best thing you can do is find someone with a large pond that can take them, they'll be much happier & healthier.