First, break out beer.
Second, remove motor from AquaClear/Fluval C.
Third, remove impeller.
Fourth, lube the shaft inside the motor. (Put a small glob on the end of the shaft, the impeller push it down the rest of the shaft when you install it.)
Fifth, install impeller on to lubed shaft and slide back down into the motor.
Sixth, install motor back onto the AquaClear/Fluval C.
Seventh, break out another beer and enjoy the silence.
ok, I've realized I used the word lube and shaft too many times for one day.