try this, if you have removed the impeller and cleaned it as well as the little hole it fits in and you still get the rattleing noise, this may sound kinda strange but take some well chewed bubble gum and apply a small amount to the rubber bushings on each end of your impeller. don't put a lot on as it will get into the impeller. my filter did the same thing, i put the gum in it about 3 1/2 yrs ago, no problems since. tightens up a loose fit and is non permanent.