Aqua-Cs dont' make a sound. As far as turning it off and on, lots of people do it, however just so you are aware, if the conditions are right the "dead" water inside the skimmer column can get really nasty really fast and then be pumped back out into your main tank once you kick the skimmer back on.
Here's to swimmin with bowlegged women.
Reef with 30G Sump/Fuge Combo
-30G LTAnemonarium with mated porcelain crabs, 10 sexy shrimp, and 2 pink skunks all tied into the other 135G in my system.