I bought a Reef Octopus Classic 90 HOB Protein skimmer like 2-3 months ago and it worked great for like 2 months but about three weeks ago it started making a strange suction sound so I broke it down and cleaned it and set it back up and worked great for another two weeks now it's back making the same sound and was wondering if anyone can think of any problems it might have. (The sound is like it's trying to either suck up air or water and have trouble doing it) the skimmer continues to work great but the sound has me worried. Thanks for any help.