i bought 2, 1 had a bad impeller, pumped fine but banged around a lot, i took that one back and the replacement one did the same thing, i switched impellers with some old 110's i have and the problem followed the new impeller, i call hagan about this and they needed me to fax over the reciept and they are sending me 2 new impellers, i told them the noise was coming from both, these were purchased at petsmart, and yes i will be returning the broken one after i get the 2 new impellers, i will save those as spares, the filter works fine if you turn the flow control all the way down, but when you turn it all the way up, it starts banging, i believe it is quality control from the manufacturer, not refurbs being sold