Quick Answer:
If you hear a sharp whistling or squealing that stops when a supply valve is opened fully, the most likely causes are a partial restriction or a vibrating component that changes behavior at different flow speeds. Do a few simple checks yourself—listen while opening the valve halfway, then fully, to compare the pitch and identify if a partial restriction creates resonance. If the sound continues after these checks, a plumber can safely find the exact restriction and fix it.
Why This Happens
When a valve, aerator, or narrow point in the pipe forces water through a smaller opening, the higher-velocity flow can create a high-pitched whistle or a squeal. That noise often changes or disappears if you change the flow speed: at a certain speed the parts stop vibrating in the same way, so the noise goes away.
Common sources include partially closed angle stops, worn valve seats, loose packing or washers, and clogged aerators. External events can also introduce debris or change pressure conditions—see Whistling started after city work if the timing matches nearby main work, or check Screeching after replacing angle stop if you recently changed a supply valve.
Step-by-Step What to Do
1. Locate the noisy line
- Try to pinpoint whether the sound comes from a single fixture (sink, toilet, washing machine) or from multiple outlets. Is it only when a particular valve is partly open?
- Listen near visible valves and supply lines; hold a cardboard tube or a paper towel roll to your ear to help localize the sound if needed.
2. Compare valve positions
- With the fixture on, open the suspect valve halfway and listen to the pitch and loudness.
- Then open the valve fully and compare. Note whether the pitch drops, the volume falls, or the noise stops entirely. This quick comparison helps identify whether a partial restriction creates resonance.
3. Check nearby fittings
- Turn the fixture off and remove the aerator or strainers on faucets to check for debris. Clean them and test again.
- For angle stops (under sinks), cycle them open and closed a few times gently to see if a stuck washer shifts. Do not force them if they are stiff.
4. Isolate the problem
- Shut off other nearby valves one at a time to see whether the noise changes. This can help locate the exact valve or branch causing the sound.
- If shutting a particular valve makes the noise stop even when other fixtures are used, that valve or its downstream fitting is likely the source.
5. Record what you observed
- Note which valve position changed the sound, whether the noise was constant or intermittent, and whether it appears only when other appliances run (dishwasher, heater, etc.). These details will help a plumber diagnose the issue faster if you call one.
What Not to Do
- Don’t leave valves partially closed long-term. That stresses the valve and piping and often keeps the restriction that causes noise in place.
- Don’t try to “tune” or fix resonance by random tightening or makeshift shims—resonance issues are better tuned by a plumber with the right tools and experience.
When to Call a Professional
Call a plumber if:
- The noise continues after the basic checks above.
- You can’t locate the source, the valve is hard to operate, or water is leaking.
- The sound started after pressure changes, nearby city work, or replacement of a valve and you want a safe inspection.
A plumber can measure pressure, inspect valves and pipes, remove and replace worn parts, and address resonance without risking damage to the system.
Safety Notes
- Do not force stuck valves. Forcing can break the valve and cause a sudden leak or water damage.
- If you must shut off the main to prevent damage, do so carefully and follow your home’s procedure for draining lines if recommended by your plumber.
- Avoid disassembling pressurized valves or cartridges yourself unless you have experience. Closing the supply and relieving pressure first is essential.
Common Homeowner Questions
- Why does the noise stop when I open the valve fully? — Changing the flow speed alters how parts vibrate; at full flow the vibration that caused the noise often stops.
- Can I leave the valve fully open as a permanent fix? — Not recommended; it may change how the system operates and mask an underlying issue that should be fixed properly.
- Will a plumber need to shut off my water? — Possibly. Some diagnostics and repairs require shutting off water to that branch or the main to work safely.
For more related articles, see the Whistling or Screeching Noises in Pipes hub.