Depends on the exact nature of the noise .... if it is a 60 Hz hum, it is from the electronics/coils & the only thing you can do is to isolate it so it won't be transmitted as much. (eg placing the pump on a piece of foam, use flexible pipes, enclosing the sump, etc)
If it is more mechanical .... then I would suggest cleaning out the impeller. I had a used Magnum that must have gotten sand in it at some point, and there are grooves worn into the impeller magnet & the housing, so the thing rattles a bit & make noise. You might improve things by cleaning &/or replacing the impeller. But if the housing is really worn, there is not much you can do.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.