[Myka]

DC pumps are definitely quiet. For AC pumps, Eheim are on par with DC. I have an Eheim Compact 3000 for a return on my own tank, and when I turn it on after a water change I have to look to see if there's flow because I can't hear it kick in. Unfortunately, Eheim aren't very big, so they aren't a good choice for large reefs. In a "silent" setup, the noisiest piece of equipment will always be the skimmer because of the air suction. The best thing you can do is choose a skimmer with a quiet pump (duh), and make sure it has an air intake silencer on it. I have an ATB skimmer which uses an Eheim 1250 or 1260, can't remember. There is a silencer on it, but I find it's quieter in the winter when I have a CO2 scrubber attached to it (I use a TLF canister with 1/2" hosing). If a silencer is noisy, you can often quiet it down by running a larger diameter airline hanging off the silencer since most of the noise is the suction of air through the end of the small airline.