[iggiebee]

From the notes of an aquarist:

There are an additional two things to check for besides (read before) the crazy glue mode.

1) The impeller's (stainless steel) shaft has two rubber seats or cushions, one at each end. If you disassembled the pump and misplaced one or both, and/or did note properly seat the shaft, it will surely rattle when the pump is turned on.

2) If there is the smallest amount of dirt in the shaft, the impeller will tend to rattle. To test for this remove the impeller assembly, give it a good rinse in water, and make it spin while grabbing it between thumb and forefinger of one hand; it should spin freely like if it was on roller bearings. IF does not spins freely, then you need to take it apart and clean everything under water using an old tooth brush.