Quick Answer:

A high-pitched whistle when the sink is on usually comes from fast-moving water passing a small gap or restriction. Start by checking the aerator seating, inspect the shutoff valve washer at the angle stop, and reduce system pressure if needed. These three checks fix most cases without calling a plumber.

Why This Happens

Whistling is a vibration caused by water flowing quickly through a narrow opening. Common places for that to happen are the aerator, the faucet cartridge, or the shutoff (angle) valve. Mineral deposits, a mis-seated aerator or O-ring, a worn washer in the shutoff valve, or high water pressure can create the tiny gap and the whistle sound. If the faucet is hard to operate, that can point to internal buildup or worn parts and may be connected to the same issue—see how a stiff handle relates to the noise in the section below.

Step-by-Step What to Do

1. Confirm the source

• Turn the faucet on slowly and listen closely. Note whether the sound comes from the spout, from under the sink near the shutoff, or from the faucet body.
• Try the hot and cold separately to see if one side is louder. This helps narrow the part to inspect.

2. Check the aerator seating

• Unscrew the aerator from the tip of the spout. Use a cloth to protect the finish and pliers only if it’s stuck.
• Inspect the screen and the rubber O-ring or seat for debris, mineral build-up, or damage. Clean the screen with vinegar or a brush.
• Check the aerator seat in the spout for nicks or a warped edge that would let water whistle past. Reinstall the aerator gently and hand-tighten only.

3. Inspect the shutoff valve washer

• Locate the angle stop under the sink and turn it fully off, then open the faucet to drain remaining water.
• With the supply off, open the valve slightly to see if the noise appears when operated. If the angle stop makes noise or feels rough, the internal washer or seat may be worn or have debris.
• If comfortable, remove and replace the small washer or the whole angle stop. If you’re unsure which washer to buy, note the valve type or take the part to a hardware store for matching. If replacing, make sure the water is off and test carefully after reassembly.

4. Reduce pressure

• Measure or observe house pressure if possible. If pressure is above about 60–80 psi, high pressure can make or worsen whistling.
• As a simple test, partially close the sink shutoff slightly (turn clockwise a fraction) and check if the whistle stops. If it does, high system pressure or a worn part is likely the root cause.
• For a permanent fix, have a pressure regulator adjusted or installed at the main if household pressure is too high. Do not fully close supply valves to control pressure long term—use proper pressure regulation.

5. Test and follow-up

• After each change, run the faucet at normal flow and listen. If the whistle stops, leave the part you adjusted in good condition and monitor for recurrence.
• If the problem returns or you find corrosion or damaged internal parts, replacement of the faucet cartridge or angle stop may be needed.

What Not to Do

• Do not over-tighten aerators. That can strip threads, crush O-rings, or warp the seat and make the problem worse.
• Do not force a stuck valve without shutting the main supply first. Forcing can break fittings or cause leaks.
• Do not attempt to adjust a house pressure regulator if you’re unfamiliar with it; incorrect settings can harm appliances. Call a pro for PRV work.

When to Call a Professional

Call a plumber if:

• The noise persists after aerator and shutoff checks.
• You find corroded or damaged internal parts you can’t safely replace.
• House water pressure is high and needs a pressure regulator installed or adjusted.
• The shutoff under the sink leaks, breaks, or you can’t turn it off fully.

A professional can diagnose hard-to-find sources (like a worn cartridge inside the faucet) and handle PRV work or valve replacement safely.

Safety Notes

• Always shut off the supply valve and relieve pressure by opening the faucet before disassembling valves or aerators.
• Protect chrome and finishes with a cloth when using pliers. Use the correct tools to avoid damage.
• If you smell gas, see major leaks, or suspect a serious plumbing failure, stop and call an expert immediately.

Common Homeowner Questions

• Why does it only whistle on one side (hot or cold)? Often the issue is a worn washer or debris in that side’s valve or cartridge; test each side separately to isolate it.
• Will cleaning the aerator usually fix the whistle? Cleaning the aerator and seat often fixes mild whistling caused by debris or mineral build-up.
• Could high house pressure cause other problems? Yes—high pressure can shorten the life of valves, cause leaks, and stress appliances; have a plumber check and install a regulator if needed.

If the whistle is brief and cleared by cleaning the aerator, keep an eye on it. If it returns, the next likely steps are replacing the angle stop washer or addressing water pressure. For more on related issues, see the article on low water pressure at this sink and the guide about a faucet handle hard to turn.