dont know whats up with your hot magnum. mine isnt loud. i would look for a canister filter. as soon as the water drops a little with hobs will be louder then the hob.
My Penguin 350 is silent if I have it all cleaned out and the water level up. I've had other HOBs that were noisey, mainly whispers when I first started out. if you dont mind spending a little extra, have you considered getting a smaller eheim canister?
Prime reeks seriously. thats its only downside IMO. :barf::thud: