NoiseCurbMost household noises are harmless, but four mean act now: a carbon monoxide alarm, a gas smell, buzzing or crackling from electrical outlets or panels, and a boom when a gas furnace or water heater starts. CPSC advises a CO alarm meeting UL 2034 in every home and a yearly professional inspection of fuel-burning appliances. For other sounds, use the lookup table and record the noise for a technician.
Homes make noise. Most of it is harmless: a fridge humming, pipes ticking as they warm up, a fan whirring. A few sounds, though, are warnings you should never ignore. This guide is a lookup table: find the sound you hear, see what usually causes it, what you can check yourself, and when to stop and call a professional.
First: the sounds that mean stop
Carbon monoxide deserves special attention. The US Consumer Product Safety Commission (CPSC) reports that more than 200 people die each year from unintentional carbon monoxide poisoning linked to consumer products that is not caused by fire, with home heating equipment a leading contributor. CO has no smell. Early symptoms feel like the flu: headache, tiredness, shortness of breath, nausea and dizziness. CPSC's advice is that every home should have a CO alarm meeting the UL 2034 standard, and that fuel-burning appliances should be inspected by a professional every year rather than serviced by homeowners.
The lookup table
| Sound | Where | Common cause | What you can check | Call a pro? |
|---|---|---|---|---|
| Boom or bang at startup | Gas furnace | Gas building up before lighting (delayed ignition) | Nothing inside the unit; note when it happens | Yes, promptly |
| Pops and ticks as heat comes on | Ductwork | Metal ducts expanding and contracting | Whether it only happens at start and stop | Only if loud or new |
| High-pitched squeal | Furnace or air handler | Worn blower bearing or belt | Whether it gets worse over time | Yes, soon |
| Humming but not running | Outdoor AC or heat pump | Often a failing start component or motor | Breaker, thermostat setting | Yes |
| Loud bang when a tap shuts | Water pipes | Water hammer: fast-moving water stopping suddenly | Whether it happens with one tap or all | Usually a plumber, not urgent |
| Popping or rumbling | Tank water heater | Often sediment at the bottom of the tank | Age of the heater, how often it is flushed | Yes, for gas units |
| Buzzing or clicking | Refrigerator | Normal compressor and defrost cycles; loud buzz can mean a failing fan | Whether coils are dusty; whether it is level | Only if very loud or not cooling |
| Whistling | Air vents or ducts | Air squeezing through a small gap or closed vent | Whether vents are open and filters clean | Rarely |
| Buzzing or crackling | Outlet, switch, panel | Loose connection or overload | Nothing; stop using it | Yes, urgently |
The explanations in the table are the common causes technicians report; the actual cause in your home can differ, so when in doubt, get it checked.
Heating equipment
Gas furnaces made since 1987 include flame roll-out protection, according to CPSC, and later standards added shut-off protection for blocked vents. That is reassuring, but it does not replace an annual inspection. A startup boom in particular is a sign to call a professional rather than wait. Our detailed guide to a noisy furnace explains each sound and what to do.
Plumbing and water heaters
Water hammer is the loud knock you hear when a faucet or washing machine valve shuts quickly. It is usually a nuisance rather than a danger, but repeated shocks can stress pipes and fittings, so it is worth asking a plumber about arrestors.
Popping from a tank water heater is commonly caused by sediment collecting at the bottom. For gas water heaters, remember that they are fuel-burning appliances covered by CPSC's advice on yearly professional inspection.
Cooling and fans
A humming outdoor unit that does not start, a grinding sound or a sudden change in noise usually needs a technician. For general loudness from a working unit, placement and maintenance make a difference, which we cover in our guide to a loud AC or heat pump.
Kitchen appliances
Refrigerators cycle on and off, click when defrost timers switch and hum when the compressor runs. Those sounds are normal. Loud buzzing, rattling or grinding, especially if the fridge is not cooling well, points to a fan or compressor problem.
A simple habit that helps technicians
Record the sound on your phone, note the time and what was running, and play it to the technician. Intermittent noises often stop the moment a professional arrives.
Myths worth dropping
- "A boom when the furnace starts is normal for old units." It is a reason to call a professional.
- "No smell means no carbon monoxide." CO is odorless; only an alarm will tell you.
- "Popping water heaters are fine forever." It is usually sediment, and gas units should be inspected yearly.
The short version
Most household noises are harmless, but a CO alarm, a gas smell, electrical buzzing or a startup boom mean stop and call for help. Fit a CO alarm meeting UL 2034 and have fuel-burning appliances inspected every year. For everything else, use the table, record the sound and decide whether it is a nuisance or a job for a professional.
Questions people ask
Why does my furnace boom when it starts?
Often gas builds up before lighting, called delayed ignition. Treat it as a reason to call a professional promptly.
Is water hammer dangerous?
Usually it is a nuisance, but repeated shocks can stress pipes and fittings. A plumber can fit arrestors.
Why is my water heater popping?
Commonly sediment at the bottom of the tank. Gas water heaters should be inspected yearly.
Can a noisy furnace leak carbon monoxide?
A noise alone does not prove it, but any fuel-burning appliance can produce CO if faulty. Carbon monoxide is odorless, so fit a CO alarm and have heating inspected every year.
Sources
- Home heating equipment and carbon monoxide · CPSCchecked
- CPSC urges annual fuel-burning appliance inspection · CPSCchecked
- Install a carbon monoxide alarm; annual furnace inspection · CPSCchecked