I'm currently running a reef octo dc10500 and love it. Dead silent, adjustable flow, little to no heat, and half the power consumption of the mag 18 I was using.
For sound comparision I hear my wp25's across the room very faintly, at about 2' from tank I can hear the over flow, cleaning the glass I can hear the skimmer, if I stick my head in the sump area I still can't here the dc pump.