in the top part that looks sealed has a black snout poking out - if you twist that you should be able to get it out and at the impeller to see why its noisy - may have picked up some grit or plant material and got wrapped around the impeller shaft....
if you cant get to it... just take filter into aquotix and im sure a friendly staff member will help you
i have 3 astro cannisters and they never miss a beat... but you do need to clean up the impeller and its hole for any crap thats built up over time in there....
very simple setup really - and it works well... once you are able to remove impeller you can do all your own maintenance... might be a good idea to clean the inside of your hoses while your there... with a spring brush or pipe cleaning tool... or even a rolled up piece of scouring pad flushed through using pressure from your mains tap...