Oh right right. I've since stuck some valves in the caps I made there with airline tubing. That cut the gurgling 100%. My noise is in the actual box and by the spray bar. Filling the box up kills all the noise BUT what it does is overflow my very small sump with a power out. So I'm back to the very tight balance I spoke of. Again... newbie design. Without the refugium I would have more room to play with volume. I cut that wall down 1" to allow for some additional overflow. I think I'm going to cut some slots in there this weekend to bring it down even more.
On the spray bar, if you look at the plexiglass enclosure I made, I just put a folded towel over it and it muffles the sound pretty good. I am thinking about going up and getting some pipe insulation to wrap the down tubes in. That might kill some of the rush noise a bit too. Plus it will keep my water warm right?