Yeah they can be, I'm trying a few tricks to reduce the noise as much as possible. The problem you get is that with a gravity fed system, flow rates change due to prefilters becoming dirty etc. This changes the water flow dynamics slightly and what was a very quiet system yesterday, may start sucking air today and making strange noises - so you need to adjust things again to quieten it downPeteJ said:Looks very professional! i do have a question for you though, do you find your trickle filter particularly noisy?