Hi,
i just started a new a new reef tank and wanted to share my experience with noise. I am using a Eden 135 pump. I was told that this was quiet relative to a skimz pump that I bought and returned. Initially, the Eden was quite silent but became noisy after I attached my chiller to it. Reading thru online forums, I realized that DC pumps are a class about AC pumps as far as noise is concerned. Well, too late for me since I already bought my pump. So I started to see how I can improve my setup. By chance, I detached the pump from the 4 silicon black rubber suction cups that were attaching it to my sump floor. The noise immediate went down Very Significantly. The pump is resting on top of the 4 suction cups but not attached. Isolation is the key! Very happy with the quick and simple fix. Hope this may be helpful to others.