If thats not a refugium, then yes I agree with playa cut the pipe, and put a sock on it. It has made my setup so much more quiet. I have a sump side and a refugium side, on my refugium side I have the pipe like you do, but there isn't much flow going through my refugium so the bubbles arent that bad. Most of my flow goes to my sump, then to my protein skimmer/ phosban reactor section, then to the return section.
I'll try to get a pic posted later. Though I took the idea from some on melev's reef.