I've heard a lot of theories about why we're finding vomit and I appreciate every one of them. The one I'm going on right now is that Beowulf is the vomitter and he's eating kibble too fast. I say this because he eats kibble pretty fast and because the vomit is undigested kibble.
Since finding the last glob of vomit, I have stopped giving the boys dry food to see if that helps. So far, no dry food and no more vomit. However, we can't do this indefinitely, because the dry food is a good part of their diet.