Once you get into those larger size pumps they must get louder.My Mag 7 was super quiet but the Mag 24 is loud as heck.Make sure its not noise from vibrations first.I know the smaller Eheims are quiet but not sure of the larger one.I not 100% sure on what pump ran internally and can pump 1200gph that are quiet.
Externally the little giants,Iwaki and Panworld pumps are quiet.Have you thought of one of those running outside the sump..Marine Depot and Premium Aquatics recommended a Panworld for me.They say its more affordable,runs quiet and doesn't heat up the water like some pumps.