Why is my furnace making a loud noise?

By Dana Whitlock. Updated October 2026. Repair or replace?

Furnace noises are clues, and the type of sound narrows things down. Whistling usually means an airflow restriction. Rattling often means a loose panel or duct. Grinding or squealing comes from the blower motor. A loud bang when the burners light is the one to take seriously. Carrier says it points to a clogged burner and needs professional diagnosis.

Likely causes

Whistling from a clogged filter or duct gaps Safe to check

Carrier links whistling to a clogged filter or gaps in ductwork. Air squeezing through a small opening makes the tone. A new filter is the first test.

Rattling from loose panels or ducts Safe to check

A cabinet door not latched or a duct section that has shifted will buzz and rattle when the blower runs. You can push the furnace door closed and look at exposed duct joints.

A bang or boom at ignition Pro job

Delayed ignition lets gas build up before it lights, causing a small boom. Dirty burners or a weak igniter are the usual causes. Do not run the furnace again and again to test it.

Squealing or grinding from the blower Pro job

Worn motor bearings or, on older units, a slipping belt make a high squeal or a grinding noise. Work on the blower means cutting power and opening the cabinet, which is a technician's job.

Ticking or popping ducts Safe to check

Sheet metal ducts expand and contract as they heat and cool, making ticks. This is usually normal.

Safe things to check first

• Note exactly when the noise happens: at ignition, while the blower runs, or after shutdown.
• Replace the filter if it is dirty and listen again.
• Make sure the furnace access door is seated and latched.
• Look at exposed ductwork for disconnected or sagging sections.
• Keep anything that can burn at least 3 feet from the furnace, as the U.S. Fire Administration advises for all heat sources.

When to stop and call

Call a licensed HVAC technician promptly for a bang at ignition, grinding, a burning smell, or any noise that comes with a carbon monoxide alarm. If the alarm sounds, get outside to fresh air and call 911. If you smell gas, leave without flipping switches and call the gas utility from outside. The USFA also recommends having heating equipment inspected each year by a professional, and that visit is a good time to raise smaller noises.

Repair or replace?

Start with its age. Type the serial from the label:

Loose panels and filters cost little. A blower motor or burner service is a moderate repair. A noisy furnace near the end of its life is the harder call. DOE's average for gas furnaces is about 21.4 years, and a 2007 builders' survey listed 18. Date yours with the age decoder above. If it is past those ages and the noise is the motor or the burners, get a replacement quote alongside the repair and run both through the quote checker.