Not sure what brand of powerhead you use that makes loud hum noise. I have both the AC powerhead and Koralia circulation powerhead, and they are absolutely silent. Canister is quieter only because it is hidden beneath the cabinet sound barrier. I have compared canister with HOB side by side, and canister is nosier. Placing the motor inside the tank provides some sound barrier effect, but if the impeller makes clicking noise, nothing helps.
True. The heavier your stocking, the more frequent you need to clean the filter and impeller. But the temptation not to stock one more fish is hard to resist. The biggest issue with magnetic drive pump is slippage. If the impeller is gunk up, it won't self start in power surge. So periodic cleaning of the impeller is a necessary maintenance requirement. But the more frequently you clean the impeller, the faster you can damage the O ring.
I agree I have power heads that are silent