Join Date: Mar 2004
Location: S.F. Bay Area, CA, USA
Have you tried running the filter without the lid on the filter housing? I've found that in more cases than not, the lids vibrate quite loudly and taking it off will take care of most of the noise. Additional noise can occur where the filter vibrates against the side of the tank or on the frame where it hangs off. You may need to wedge something between the filter and tank to dampen the vibration.
I use AZOO palm filters on two of my tanks, but I can't imagine that it's too different from the Red Sea ones. If my suggestions don't help, it could be something caught in the impeller or something.