Planted Tank Guru
Join Date: Nov 2009
Location: Missouri united states
I used the AC filter's for year's and pretty much had the science of keeping them quiet mastered.
Often times the rattling can be the top cover which can be removed or perhaps the plastic piece that rest's on the back glass outside the tank, and attaches to bottom of housing to keep it level becomes lost, or won't hold filter in position level wise, and a piece of mouse pad for computer can be cut with scissor's and wedged in place.
If filter tilt's too far forward or backward's it can affect how impeller rides on the shaft and noise can be result.
Moving the intake tube up or down slightly can help quiet the filter's along with adjusting flow which is neat feature with the AQ's.
When tuned just right,I would have to look to see if there was surface movement in the tank to know if the filter's were running.
Goes without saying ,that cleaner filter/impeller makes less noise than dirty one .
Sand was by far the hardest on the filter's as it is with all of em ,so keeping the intakes up off the substrate a fait bit helps greatly.