My recommendation before setting up any filter, HOB
or cannister, is to reseat the impeller. My Emperor 280 and both my 400's were very quiet when new, and got quieter as gunk built up. There was no rattle at all. If there's any sign of rattling, turn it off immediately and pull out the impeller unit and reseat it. The rattling could very well cause internal problems if left like that, such as slowly chewing through the plastic housing.