I also have an Aqua C Remora Pro w/ a Mag3. Once, a few months ago, I came home to the pump making a strange noise and found it making a violent sandstorm in my tank as well... similar to what others have experienced. I do not have a prefilter box to actually skim surface water, which is probably why my pump wasn't shooting water out of the tank.
Also, in reference to a question posted previously in this thread, regarding the need for a prefilter box or not (i.e. the importance of skimming the surface water vs. water six inches under the surface) and though I have no basis for comparison as I have never used a prefilter box, my skimmer has been very good at getting "crap" out of my water. Maybe the cup would fill up faster or with more concentrated waste if I skimmed the surface, but I don't think skimming under the surface makes your skimmer TOO much less efficient. Aqua C advertises that having a prefilter box increases efficiency by 20% or more.
Lastly, again w/no basis for comparison having not heard any other protein skimmers... I would say mine is "moderately" loud. In other words, it's not nearly as quiet as the advertisements would make it seem to be. But maybe I just have high standards. :yes:
I'm going to check out the Fluval surface skimmers mentioned previously... if they are really only $12, that seems like a worthwhile investment.