Right, got it you are not a new aquarist. You never know the experience level of a poster. I have helped new aquarists when they place pumps well below or many feet away from a deep tank and hear loud noise. Another reason is finding they have so many accessories like pirate chests and sunken ships that the pump is straining. But in your case, it sounds like the diaphragm is defective. Oh well. Like you, I too have been pleased with Fluval products. Perhaps contact them and see if they will assist?