External filters are largely quiet running units. If you are experiencing a lot of noise, it could be for one of two reasons;

1.) Damage to the impeller;

To check your impeller, please click here and follow the instructions. If the impeller is damaged you can find replacements here

2.) Air in the system;

To check that the unit has been primed properly and that there is no air circulating inside, please click here for instructions on how to prime your unit.