Bought first of two tanks yesterday, this one for my bedroom is four foot and has external Fluval filter. I connected everything up and have got it going but ti doesn't seem to be pumping out with the force that I expected, occasionally there is a rapid burst of bubbles out the inlet hose and a funny noise, it does mention making sure everything is connected right but it seems ok, does this sound normal or is something wrong with the set up of the filter?