After years in service (15 plus years), my trusty Eheim 2217 finally acting up. For the pass couple of days it produced loud rattle noise. I dismantle the filter, especially the impeller area and found that the shaft rubber cap was loosen due to wear and tear as well as age. This cause the impeller to miss align and after thousand or maybe million rotation, the shaft hole is giving up and become ellipse. This is where the noise coming from. The impeller was hitting the wall during rotation.
Picture of the shaft where one of the rubber cap is loose.
Impeller picture where the hole become ellipse due to continuous friction with the shaft.
Zoom in on the hole, colored in red for easy viewing.
So I replace the whole assembly, bought new impeller and shaft which cost me total S$37 (S$29 + S$8) and it silent like brand new. My advice next time when you service your filter and feel that the shaft is loose, change it.