I'm surprised that Ilikefishes and MrWhite say the Juwel filters are quiet. When I got my Rio 125, I was quite prepared to use the built in filter, but it was so noisy! I even bought a replacement pump for it after the shop said there was nothing wrong with the first one, but that was just as bad. My husband threatened to make me turn it off while he listened to his music, and when we were in bed in the room above the tank it sounded like someone running an ancient diesel car right outside the window. We put up with it for a couple of weeks, then I took it out.
I know from filters in my other tanks that they can be noisy if they are not seated properly or have air trapped, but nothing I could do would get rid of that loud hum.