Our toilet makes an annoying, low fog horn type noise every time we flush. The noise goes on the whole time whilst the cistern is filling up, except for the last few seconds. No other usage of water in the bathroom or anywhere else in the house causes a similar noise. The noise seems to resonate throughout the house.

What could be the cause of this and how might we go about trying to diagnose and fix it?

There is a recording of the noise here, though the droning noise seems quiet in the recording, as it's overwhelmed by the cistern filling noise: https://drive.google.com/file/d/0ByIxRsvAvipMdlNxMUhtT1dORFFyMTJvYmt5eGxfVVcxdmJj/view?usp=drivesdk

  • 1
    Make sure the shutoff valve for the toilet is fully open.
    – JACK
    Commented Dec 10, 2019 at 13:05
  • Restriction of water flow can make some awful noises. Follow Jacks advice on the shut off valve. Also take a picture of the fill valve in the tank. some types are prone to make more noise than others.
    – Kris
    Commented Dec 10, 2019 at 13:52
  • Are close to the coast 🤓
    – Ride Sun
    Commented Dec 11, 2019 at 5:17

1 Answer 1


There's a valve. It's called a "fill valve". It has a float, and its job is to add water to the tank until the bowl reaches the designated fill level.

It sounds like your sound is happening at exactly the same time the fill valve operates at full speed.

Fill valves are $10.

  • So should I be restricting or making sure the fill valve is operating at full speed?
    – Sam Holder
    Commented Dec 11, 2019 at 16:24
  • 1
    @SamHolder Either one is fine provided it makes it stop howling. What I'm saying is they're $10, so I'd just replace it... Commented Dec 11, 2019 at 17:46
  • Thanks, finally got the time to do this yesterday. when I manually varied the fill rate with the old valve it didn't really seem to affect the noise, slower was quieter but I had to go really slow to make it stop. Changed the valve and water fill rates seems the same but now no noise at all. Even adjusting the fill rate manually to slow it down doesn't seem to make any difference - I can't make it make a noise now! Much appreciated!
    – Sam Holder
    Commented Jan 6, 2020 at 17:18

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