Why does my heating system make a popping noise?

Heating system popping is usually caused by the thermal expansion of sheet metal ducts. When hot air rushes in, the cold metal expands rapidly and pops outward.

Why do my vents make a burping sound?

Burping or gurgling sounds from vents often indicate issues with the condensate drain line (water trapped in the pipe) or refrigerant lines moving through the walls.

HVAC and House Burping: How Your Heating and Cooling Cause Noises

Your Heating, Ventilation, and Air Conditioning (HVAC) system is the lungs of your home. It moves massive amounts of air through metal tubes hidden in your walls. As explained on our homepage, when you force hot air into cold metal, physics takes over.

HVAC house noises are the most common source of complaints for homeowners. The sounds range from metallic bangs to rhythmic gurgles. While often annoying, these sounds function as an early warning system for the health of your machine.

Top 5 Reasons Your HVAC Makes Noises

If your furnace or AC is acting up, it usually falls into one of these five categories of heating system pops and groans:

Thermal Shock (Duct Expansion): When a furnace blasts 120°F air into 60°F sheet metal ducts, the metal expands instantly. This rapid expansion causes the metal to pop loud enough to wake you up.
The "Oil-Canning" Effect: If your ducts are undersized or the metal is too thin, the change in air pressure when the blower starts can suck the duct walls inward, creating a booming sound.
Condensate "Burping": AC units produce water (condensate). If the drain line is clogged or not vented properly, water can get trapped, creating a literal gurgling or burping sound as air bubbles pass through it.
Dirty Filters (The Gasp): A clogged air filter restricts airflow. The system has to work harder to pull air in, often resulting in a high-pitched whistle or a "gasping" sound when the cycle ends.
Loose Brackets: Vibration from the motor can loosen the straps holding your ducts to the ceiling joists, leading to a rhythmic rattling or squeaking.

Diagram showing metal ductwork flexing or 'oil-canning' due to pressure changes — Metal ducts expand and contract ("oil-canning") when pressure changes, causing loud popping sounds.

Diagnosing the Sound: Burp, Creak, or Pop?

Your HVAC system speaks a specific language. Here is how to translate it to determine if it is normal.

The HVAC Burp (Gurgle)

Sound: Bubbling water or a "glug-glug" noise.

Cause: Refrigerant lines or Condensate drains.

Fix: Check your AC drip pan. If it's full, you have a clog.

The Duct Pop (Bang)

Sound: A singular loud metallic bang, usually when the heat turns on or off.

Cause: Air duct expansion.

Fix: This is often harmless, but insulating ducts can muffle the sound.

The Furnace Creak (Tick-Tick)

Sound: Repetitive ticking like a clock.

Cause: Metal blades heating up or fan balancing issues.

Fix: If it gets louder, it may be a failing motor bearing.

DIY HVAC Checks

Before calling for help, try these simple steps to reduce the noise:

Replace your air filter immediately.
Walk around and ensure all supply vents are open (closing too many increases pressure and noise).
Listen near the furnace unit—if the sound is internal (grinding/screeching), turn it off.

If the noise persists or you smell burning, it is time to bring in an expert. Read our guide on When to Call a Professional.