Usually when an Aquaclear is noisy you have to change the impeller shaft. Pull off the motor, look at the shaft - it should be a straight up and down cylinder but when worn gets more of an hourglass shape or even uneven wear/indentation in the shaft itself.
To change it, rock it back and forth with pliers firmly but carefully and it should come right out of the motor.
Put the new shaft in and tap it to seat it Put the impeller back on.
It may be noisy for a few hours until enough grime builds up to make it run smoothly.
I've not had to change impellers yet on any of my Aquaclears and they are several years old. Usually the impeller shafts do the trick and they are only a few dollars each.