toilet fluidmaster resized 600A toilet refilling shouldn’t make unusual noises. What I commonly see is as a toilet is refilling with water the problem is with the float at the fill valve.

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The old ballcock style is famous for these types of noises. As the tank fills, the float will rise to the point that it shuts off, but it never quite shuts off. Instead it will repeatedly stop and start the water making a “bang bang bang” sound. It’s really more of a loud stuttering sound. You can try to bend the arm downward (toward the water) to get it to shut off earlier, but generally when they start behaving like that, it’s time to replace them.

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A fluidmaster is a better design (and takes less space), but the noisemaking can also happen with it. It seems once they get old they get to the point where they just don’t quite shut off and you get the noises.

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I would recommend replacing the fill valve with a fluidmaster. While you are at it, also replace the flapper. You can buy these items separately, but they are cheaper if you buy them in a kit, plus it will only take you 15 minutes to replace them.

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