Koi-lo wrote:

$$ Aquaclears are generally very quiet. Can the impeller be worn out?
You can try replacing it with a canister. I have a Fluval that is all
but dead silent from a few feet away. For extra silence you can set it
in a bucket and surround it with old towels or those small toss pillows
sold everywhere these days. If worse comes to worse you can always move
the tank to another wall that wouldn't be right above her head.

I have large external Fluval filters of different vintages, and
Aquaclears. Both can make slight rattly noises, although otherwise
they're great filters.

As noted in another post, the quietest filter I've had was a
within-the-tank Fluval filter. I used a foam sleeve instead of the
disposable cartridge media for this filter, to preserve bacteria and
reduce costs.

Steve