Hi Swfish,
I can't offer any suggestions for the pump noise, but your gurgling sounds like the same trouble I and many others at The Reef Tank have had, which have been solved in many variations of a few basic solutions. The trouble is, from your descriptions, I'm still not clear on how your overflows are configured. I can imagine two different schemes, each of which would have a slightly different solution, so let me describe them to you and a proposed solution and see if one of them works.
As Doug suggested, I am assuming you do not have an overflow box(es) in your tank. It actually probably doesn't matter, but being clear on that may help.
The most likely description of your overflow plumbing is that your 2" bulkheads are drilled through the top of your tank at the back (or side.) Then you have attached a 90-degree elbow to the fitting on the inside of your tank, and put a screen on the open end. If you turn the elbow so that the opening and screen point straight down into your tank, the water fills up past the opening until it overflows up into the bulkhead fitting into your tank. (The lip of the bulkhead is probably about 1" higher up than the opening of the elbow in this case.) At this point, the water drains very rapidly - and probably with much splashing - into your sump until the water level in the tank falls below the opening of the elbow, at which point it makes a great sucking sound and starts over again.
So to avoid this problem, it sounds like you have rotated the elbows so the opening in the elbow is essentially sideways, and the water level stays pretty constant but there is a constant loud gurgling noise.
The other possible arrangement is that the bulkheads come through the bottom of your tank, and you have put a piece of pipe into the bulkheads that extends up near the top of your tank, where you want the water level to be. At the top of the pipe, you have attached a 90-degree elbow with a screen, and the water drains through that. I don't think this is what you are describing though; I can't figure out any way that rotating the elbow would make any difference at all - unless you use two elbows on the top of the pipe, which would make this configuration problem very similar to the first configuration I described above.
If either of these descriptions is accurate, it sounds like you have a siphon issue if the pipe is pointed straight down and just a noise issue if the opening is sideways. This is the same problem described and solved by Richard Durso. (See his description/solution at
http://www.rl180reef.com/frames.htm.)
In your case, if one of these descriptions are accurate, you can solve your problem by rotating the input opening so that it is fully submerged, and then drill a hole in the plumbing in the top of the elbow - either one that is inside your tank, or in the plumbing outside your tank where I presume that you have another 90-degree elbow and pipe extending down to you sump. As Durso suggested, a small air valve allows control of airflow through this hole, which in turn offers some control of water level.
I actually have the second case above. I do not have an overflow box by design. I designed my overflow pipe to enter through the bottom of the tank, the fittings at the top of it to work as a screen (like the fingers on an overflow box, and to have an underwater overflow intake to reduce noise as Durso described. I also made it easy to service. It's a bit more complicated than Durso's design, but I don't lose tank volume to an overflow box and I have no fittings/equipment on the back of the tank so I can put my tank flush against a wall.
Durso's design, by the fact that the drain pipe now extends close to the top of the tank instead of draining at the bottom of the overflow box, effectively eliminates the functionality of an overflow box, except for screening out material from falling into the overflows. One function an overflow box performs is removal of surface scum. Without Durso's device, the scum would normally drain into the sump and out the holes in the bottom, where it is presumably filtered from the water in a sump or similar device. With Durso's device, the surface scum will now accumulate in the overflow box because the water intake is underwater, and the scum floats on top. Without an overflow box, and a submerged overflow intack, the scum just accumulates on the surface of the tank water. In either case, I feel it is necessary to remove this scum by some way. I did this by directing one nozzle of my tank returns in such a way that the scum was sucked under water by the natural vacuum created by the moving water, and that flow was partly directed to flow near the underwater intake. The underwater intake then sucks up the scum and takes it to the sump, where it is filtered normally.
Hope this helps. If I am totally off-base in understanding your design or you want more details on mine, please feel free to respond or e-mail me.
Glenn
