I purchased an Octopus NW-150 today and was very excited to set it up and remove my old CSS 65. However, once I got the skimmer assembled and installed, I plugged it in and very little happened. There was a short burst of bubbles then... nothing. I pulled the pump out and tested it in a tub of water and it appears to be cavitating. The impeller tries to spin, but it never fully engages. Is there anything I can do to remedy this, or am I looking at returning the pump for a replacement?