Take the filter apart and make sure that the impeller is seated properly in its housing and the housing cover is on properly. Next make sure that the intake tube is properly set in place and slipped onto the opening at the top of the impeller cover. Once its assembled properly, I fill the filter reservoir with water and start the filter. It will make a little noise as it gets all the bubbles out of the intake tube but then it should settle in and run quietly. If the intake tube allows any air into it because of loose joints, that could keep it from priming properly.