What Causes Water Pipes to Hum?

You may find the humming sound of your water pipes annoying -- especially if it's more like a hissing than a humming -- or it may find it strangely reassuring, as if it were the distant sound of meditation chants. Don't be lulled into complacency; the sound usually means that water is flowing in the pipes, and if that's happening when everything is off, it may mean you have a leak, although more often than not, someone just forgot to turn off a faucet. In any case, you could be losing precious water, so a thorough investigation is in order.

Pressure Problems

High water pressure in your pipes can make them vibrate, and the remedy is usually simple. To check the pressure, screw a pressure gauge into an outdoor faucet. If the pressure is greater than 60 pound per square inch, reduce it by turning the screw on your household pressure reducer anticlockwise or, if you have a well, lowering the cut-off pressure of the water pump. The adjustment requires you to expose the terminals of the pressure switch, which operates at 240 volts. Adjusting your pressure pump is a job for a licensed plumber or electrician.

If the pressure is 60 pounds per square inch or below, humming is caused by movement of water through the pipes, and you need to find out why.

Narrow the Search

It's Coming From the Bathroom

The humming may be audible in the bathroom or in an adjoining bedroom. If so:

• Check all the faucets, including the sink, tub and shower. Even relatively small drips can produce enough water flow in the pipes to cause cause humming. 
  
• Look under the sink. One of the faucet supply lines may be leaking.
  
• Lift the toilet tank and look inside. If the fill valve has a small leak, the tank level might be high enough for water to spill into the overflow tube, even if the valve isn't making a sound. This is common with older ballcock-style valves; if you have one of these, and it's leaking, it's time to replace it.
  

It's Coming from the Kitchen

Humming sounds that originate in the kitchen could come from the faucet or from any appliance that uses water, including the dishwasher and refrigerator.

• Look for dripping from the faucet. 
  
• Check inside the cabinet under the sink. 
  
• Pull the refrigerator away from the wall and look behind it. The tube that connects the refrigerator to the water supply has a compression coupling, and these can leak if misaligned when moving the refrigerator to clean it. The water may be spilling behind the wall instead of pooling on the floor, where you can see it.
  
• Inspect under the dishwasher by pulling away the toe kick and shining a flashlight underneath. 
  

It's Coming from the Basement or Laundry Room

It isn't common for the washing machine connections to leak, but it's possible. It's more likely that a some other faucet or valve is responsible.

• Check the washing machine connections. If either is loose or damaged, you'll see water spraying.
  
• Inspect the water heater temperature and pressure relief valve. It could be spraying water, and if so, turn off the gas or electricity to the heater and call a plumber immediately. Excess pressure in the water heater is dangerous.
  
• Look for dripping from any other faucets in the basement or laundry room.
  
• Check the outdoor faucets for dripping. The pipes that supply them usually run through the basement or crawl space. You may find that someone just forgot to turn off a garden hose. 
  
• Walk around the yard and look for soggy spots in the grass if you have a sprinkler system. They signify leaks in the irrigation pipes. You may also find water spurting from a damaged sprinkler head.
  

You may hear humming only when you're in the bathroom or the kitchen, but some leaks may cause water to flow through more than one branch pipe -- or even a main pipe, and the humming may be audible in several rooms. Pinpointing the source of the sounds you hear goes a long way toward finding the leaky or open valve.

I Can't Find a Leak or Open Valve

If you can't find the source of the humming sounds, the situation is more urgent, because it means water is leaking behind a wall or under a floor, where it can do considerable damage if you don't stop it. Look for wet or moldy drywall, pooling water on the floor or other signs of water in the house. You can conduct a more definitive test using a pressure gauge:

1. Locate a faucet outside or in the basement that is controlled by the main shut-off valve for the house. Screw a pressure-gauge onto that faucet.

2. Open the faucet and note the pressure. In most houses, it will register somewhere between 60 and 80 pounds per square inch.

3. Shut off the main water supply and watch the gauge, making sure no one uses water while you conduct the test. The needle should stay where it is, but if there's a leak, it will slowly drop toward zero as the volume of water in the pipe goes down.

4. Call a plumber as soon as possible if the test is positive or you have another reason to suspect a leak.