Do you make sure that there is not any water in the outflow tube and spray bar (if you are using that) before you fill? You also need to make sure the flow valve (if you are using that) is fully open so all of the air can escape. Then open the valve on the lid and let it fill from the bottom, forcing the air out of the outflow tube. Mine has a similar problem but it does seem to be air. I get good results by tipping the unit a bit back and forth, as well, if it is indeed an air problem. There could be a bit of crud in the impeller itself, and as I have never disassembled mine so far I am not sure how to go about doing that. Good luck, and let us know what works!