I purchased a 29 gal biocube to start a saltwater reef. After putting in the water, sand, and live rock, I plugged in the filter. It sounded more like a hacking pump than the quiet sound I expected. It seems that there is not enough water in chamber three. When I fill it with more water, it works fine until it filters it into aquarium and again it starts the loud nice. HELP!!!! Any suggestions? ( refusing to empty it and take it back) Thanks....