I'm more of an Emp400 guy, but I have had an AC before. Some general suggestion based on my experience with HOBs, if the impeller is held in place with rubber bumpers, if that rubber gets hard it doesn't stay in place as well and it might be hard to keep quiet. IIRC, the AC is like this.
People also tend to fully clean their filter to quiet it down, but in reality, the impellers are a bit more quiet once a layer of slime builds up on the impeller. If I clean a filter, I never clean the impeller (unless it gets sand in the chamber or dries with a layer of crust upon itself).