A toilet that hums or vibrates after a flush is reacting to the refill. Common causes are a debris-clogged or worn fill valve, a partly blocked shutoff valve, water hammer, or house pressure above the 80 psi code limit. Start by partly closing the shutoff valve under the tank and cleaning the fill valve.
What is the toilet actually doing when it hums?
Timing tells you a lot. Note when the noise starts and stops, because that narrows the cause faster than any part swap.
| What you hear | When | Likely cause |
|---|---|---|
| Steady hum, buzz or hiss | The whole time the tank refills | Fill valve with debris or a worn seal, or a shutoff valve restricting flow |
| Rapid banging or "jackhammer" pounding | During the refill | Resonance from a blocked or partly closed shutoff valve |
| One loud bang or thud | Right when the tank shuts off | Water hammer |
| Hum or buzz at other fixtures too | Any time water runs | House pressure too high, or a pipe rattling in the wall |
Fluidmaster, which makes fill valves, sorts toilet noise in its troubleshooting pages into a constant fill valve hiss, resonance (rapid banging or "jackhammering" in a pipe during the fill), and water hammer, a loud bang after a fill valve shuts off.
### In what order should you check?
- 1Ease the shutoff valve under the tank toward closed while the tank refills. If the hum drops and the tank still fills at a normal pace, the shutoff or fill valve is the culprit.
- 2Clean the fill valve, or replace it if it's old or scaled.
- 3If a bang comes only when the tank shuts off, treat it as water hammer.
- 4If other fixtures buzz or bang too, put a gauge on a hose bibb and read the house pressure.
Is the fill valve or shutoff valve making the hum?
Either one can, and the fill valve is the first place to look. Fluidmaster says a fill valve hiss "is alerting you that water is constantly passing through the fill valve and going into the tank." Debris on the seal inside the valve can disturb the water as it passes, and a worn valve does the same. That disturbance is what you feel as vibration.
Kohler's toilet troubleshooting sheet lists two fixes for a tank that is loud when it refills: partially close the water supply shutoff valve, and check the fill valve for debris and clean it. Kohler also says to make sure the rim feed hose is connected to the overflow and the fill valve, if your toilet has one.
Here's the short version of the cleaning routine on a Fluidmaster-style valve, which Fluidmaster describes in full on its noise page:
- 1Turn off the supply valve and flush to empty the tank.
- 2Hold the float cup up, then turn the valve cap a partial turn to unlock it and lift it off.
- 3Wipe any debris off the rubber seal and out of the valve body.
- 4Hold a cup upside down over the valve and briefly turn the water on to flush the inlet.
- 5Reassemble, lock the cap and refill the tank.
Other brands differ, so check your valve's instructions first. If it still hums, replace the valve. Our page on why a toilet whistles when it fills covers the hard-water scale that wears these valves out faster in the Valley, and how to adjust a Fluidmaster fill valve helps with setup after a swap.
### What about the shutoff valve?
That's the one people skip. Fluidmaster says that "resonance" noise means "your shut-off valve at the wall has an obstruction in the flow path of the water." Fluidmaster's water hammer page also says heavy mineral and rust buildup inside shutoff valves can cause hammer. A restricted passage makes the pipe pound while the tank fills.
Fluidmaster's suggestion is a fill valve with a built-in regulator that slows the incoming water, and if that doesn't stop it, replacing the shutoff valve. Ease the shutoff valve toward closed first. If the noise drops while the tank still refills at a normal pace, you've found it. A shutoff valve that won't move, leaks at the stem, or is crusted with mineral is due for replacement.
Is it water hammer?
If you hear a single hard bang or thud the instant the tank finishes filling, that's water hammer. The fill valve shuts fast, and the moving water slams into the closed valve. Fluidmaster says worn or damaged faucet washers, and heavy mineral and rust buildup in shutoff valves, can cause it. Fluidmaster's house-wide fix is to shut off the main, open every cold faucet from the top floor down, flush the toilets, wait 20 to 30 minutes, then turn the water back on and close the faucets low to high. That's meant to refill air chambers that have gone waterlogged.
The plumbing code addresses this too. The 2024 International Plumbing Code, Section 604.9, says "A water-hammer arrestor shall be installed where quick-closing valves are utilized," and that arrestors "shall conform to ASSE 1010." Our page on why pipes bang when you shut off water goes deeper on arrestors and pipe supports.
### What if water hammer keeps coming back?
Draining the system only helps if the air chambers were waterlogged. If the bang returns within days, the cause is usually pressure that's too high, a worn washer in a faucet, or a hammer-prone valve that needs an arrestor. Fluidmaster's own advice is to reduce the flow at the shutoff valve, and if that doesn't resolve it, to call a plumbing professional. That's a fair rule for any hammer that survives the DIY steps.
Could high water pressure be the cause?
It can, and it's the cause that hurts the rest of the house. Fast, hard-pushed water makes every valve chatter and every hammer worse.
The number to know is 80 psi. The 2024 IPC, Section 604.8, says that where pressure within a building "exceeds 80 psi (552 kPa) static," an approved pressure-reducing valve with a strainer "shall be installed" to bring it down to not more than 80 psi static. Phoenix adopted the 2024 IPC with local amendments to Sections 403.2, 410.2, 424.2 and 604.4 (Ordinance G-7397, effective August 1, 2025). The amendments we read don't change 604.8. The city's own water page says "Water pressure greater than 80 psi requires action by the home or business owner as it can damage your water pipes and appliances."
EPA WaterSense says "High water pressure can damage plumbing piping, fixtures, and appliances, and can lead to increased water consumption, premature equipment failure, and risk of leaks." It recommends incoming pressure between 45 and 60 psi.
Testing takes five minutes. WaterSense says to attach a pressure gauge to a hose bibb, the cold-water faucet for the washing machine hookup, or a cold-water faucet on the first floor, with the water fully open. If your house has a pressure reducing valve, it sits on the line near where water enters, and it can wear out. Our pages on whether you need a pressure reducing valve and the signs a regulator is going bad show what to look for.
When should you call a plumber?
Call if the noise continues after you've cleaned or replaced the fill valve and eased the shutoff, if the gauge reads over 80 psi, if you hear bangs from other fixtures, or if you see a leak at the shutoff, supply line or wall. Skip the wait if any of those is wet. HQ Plumbing & Air is licensed and insured, quotes an upfront price before work starts, and has 24/7 emergency service if something is leaking.
A chattering valve is wearing itself out, and pressure high enough to hum a toilet is working on every pipe in the house. That's the fix worth making.