The pump is definitely not likely to be the quietest piece of equipment on a tank, but if it is still audible when suspended in a container and inside a cabinet or closet, I would replace the pump, they typically last 2-3 years. They are a sealed unit and cannot be serviced, noise can sometimes come and go, for example debris snared on the impeller such as hair, threads, etc that get in just as dust, eventually break down and the pump gets quiet again, noise can also be terminal, the motor may be failing.