I had a 'noise' start in mine a few months ago. Gradually got worse until the flow started to slow, noticed wear on the impeller so bought a new one, same thing happened after a few weeks so I now have a whole new motor housing with impeller so fingers crossed this one wont clap out either. Has been a very frustrating, expensive and time consuming affair but I really like the filter so want to get it running properly. Hopefully yours is not heading the same way. Try googling 'fluval fx5 troubleshooting' it is a pdf file and pretty helpful, just a process of elimination