The fans in my biocube hood also made that "noise" so I emailed oceanic via their website and told them the problem. They sent me two new fans and after replacing them I noticed a huge difference.
i have a tank with a small blue tang, ocellaris clownfish, polys, snails, blue linka star fish, and 2 hermit crabs. My blue tang has a large tear near its anal area. The tear is white and it appears that the fish is missing some of its meat. The fish also has bumby skin around its stomach area...
i have a 29 gallon oceanic biocube with power compact and actinic lights. There is a false clown, firefish, green brain coral, war coral, orange cap montipora, torch coral, and frogspawn