Your Heat Pump Is Making Weird Noises. Here’s When to Worry (and When Not To)

Why is my heat pump making clicking, buzzing, or hissing noises?

Most heat pump noises like clicking, buzzing, or hissing are normal and caused by defrost cycles, inverter operation, or refrigerant flow. In Massachusetts winters, heat pumps run longer and adjust frequently, which creates sound. Loud, constant noises paired with loss of heat or tripped breakers should be checked by a professional.

It’s 6:30 AM, you’re making coffee, and your heat pump starts clicking like someone’s snapping their fingers in the basement. Or maybe it’s buzzing loud enough that you can hear it through the window. Or there’s this hissing sound you swear wasn’t there last week.

Welcome to heat pump ownership in Massachusetts.

We get calls about these noises constantly—especially once the temperature drops below 30°F. And here’s what we tell almost everyone: most of what you’re hearing is completely normal.

The hard part is knowing which sounds are just your system doing its job versus which ones mean something’s actually wrong.

Why Heat Pumps Are Louder Than Your Old Furnace

If you recently switched from a gas furnace or oil boiler to a heat pump, the noise difference can be jarring. Your old system had one speed: full blast. It fired up, heated your house, and shut off. Pretty straightforward.

Heat pumps work differently. They use variable-speed inverter compressors that constantly adjust their output based on outdoor temperature and how much heating you need. They also run something called a defrost cycle when it’s cold, which involves reversing the refrigerant flow to melt frost off the outdoor coil.

According to the Department of Energy, this modulating behavior is what makes modern heat pumps so efficient—but it also means more moving parts, more electronic valves opening and closing, and more sounds during normal operation

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The goal isn’t silence. The goal is predictable behavior.

Clicking Noises: Usually Normal (But Not Always)

What clicking typically means:

Your heat pump has relays, contactors, and reversing valves that physically switch during operation. Every time the system starts up, shuts down, or enters defrost mode, you might hear clicking.

In Massachusetts winter weather, defrost cycles happen regularly. When frost builds up on your outdoor unit (totally normal below 35°F with humidity), the system briefly switches into cooling mode to warm up the outdoor coil and melt the ice. That process involves the reversing valve clicking into a different position.

When clicking is fine:

• Happens at startup or shutdown
• Occurs every hour or two during cold weather
• You hear 1-3 clicks, then it stops
  
  

When clicking means trouble:

• Rapid, continuous clicking (like a playing card in bike spokes)
• Clicking followed by the system shutting down
• Clicking with no heat coming out
  
  

If you’re getting the problematic kind, something’s preventing a component from engaging properly—could be a failing contactor, a stuck relay, or a control board issue.

Buzzing Sounds: Context Matters

A low electrical hum from your outdoor unit is completely normal, especially when it’s cold and the compressor is working hard. That’s just electrical current flowing through the inverter and compressor windings.

Normal buzzing:

• Steady, low-frequency hum
• Gets slightly louder when the system is working harder
• Consistent with outdoor temperature (louder when it’s colder)
  
  

Buzzing that needs attention:

• Loud enough to hear from inside with windows closed
• Gets progressively worse over weeks
• Paired with breakers tripping or the unit not starting
  
  

Loud buzzing often points to electrical issues—loose connections, a failing capacitor, or a compressor struggling to start. Not always an emergency, but definitely worth having someone look at before it turns into one.

Hissing Sounds: Probably Just Refrigerant

Heat pumps move refrigerant through coils, valves, and expansion devices. When refrigerant changes pressure or flows through narrow passages, it hisses. This is especially noticeable when the system is ramping up or down.

Normal hissing:

• Soft whooshing or hissing during startup
• Brief hissing when the system changes modes
• Quiet hissing from indoor unit vents
  
  

According to HVAC training resources, the expansion valve—which regulates refrigerant flow—naturally creates a hissing sound as high-pressure liquid refrigerant expands into low-pressure gas.

Hissing that’s not normal:

• Loud, continuous hissing that doesn’t stop
• Hissing paired with a sudden drop in heating
• Visible ice buildup on indoor or outdoor coils
  
  

That combination suggests a refrigerant leak or a failed expansion valve. Refrigerant issues don’t fix themselves and will get worse over time.

Sounds You Should Never Ignore

While most heat pump noises are benign, a few are red flags:

Grinding or scraping: Bearings wearing out or something physically rubbing where it shouldn’t
High-pitched squealing: Usually a worn fan motor or failing compressor
Loud banging or rattling: Loose components, failed motor mounts, or something stuck in the fan

These aren’t “wait and see” situations. They’re “call someone now before a $300 repair turns into a $3,000 one.”

Why Everything Sounds Worse When It’s 15°F Outside

Massachusetts cold snaps push heat pumps to their limits. When outdoor temperatures drop into the teens or single digits, your system is:

• Running almost continuously (sometimes 18-20 hours a day)
• Going into defrost mode every 45-90 minutes
• Working harder to extract heat from cold air
  
  

More runtime means more opportunities to hear normal operating sounds. The system isn’t struggling—it’s just working exactly as hard as it needs to.

For context, the Air Conditioning, Heating, and Refrigeration Institute (AHRI) rates heat pumps for performance at 47°F, 17°F, and 5°F. Most quality systems are designed to handle these conditions, but the physics of heat transfer means they work harder and louder when it’s cold.

When to Actually Call for Service

Call if:

• A noise is new and getting progressively louder
• You’re noticing reduced heating performance
• The system is cycling on and off rapidly
• Ice is building up excessively on the outdoor unit (more than light frost)
• Breakers keep tripping
  
  

Don’t panic if:

• The house is still comfortable
• The noise is consistent and occasional
• You only hear it during cold mornings or when the system first starts up
  
  

Your heat pump has temperature and pressure sensors, control boards, and safety switches. If something is seriously wrong, the system will usually throw an error code or shut itself down to prevent damage.

The Real Bottom Line

Heat pumps aren’t quiet appliances. They’re constantly modulating, adjusting, and responding to changing conditions. That activity creates sound—clicks, buzzes, hisses, hums.

Most of these noises just mean your system is doing exactly what it was designed to do: keep your house comfortable while using less energy than a furnace.

The key is learning what’s normal for your system. If a sound is new, getting worse, or paired with performance issues, get it checked. If it’s been making that noise since day one and everything works fine, that’s probably just how your heat pump sounds.

When in doubt, a quick service call for peace of mind beats lying awake at 2 AM wondering if that clicking means your compressor is about to explode. (It almost certainly doesn’t.)

For heat pump installation, service, or just someone to tell you whether that noise is normal, give Endless Energy a call at 508-978-4996 or self-schedule heat pump service or a heat pump consultation on our website.

Quick Reference: Heat Pump Noise Guide

Save this guide. Next time your heat pump makes a weird noise at 6 AM, you’ll know whether to roll over and go back to sleep or actually do something about it.

Heat Pump Noise FAQs for Massachusetts Homeowners

Is it normal for a heat pump to make noise in winter?

Yes. Heat pumps make more noise in winter because they run longer, adjust output constantly, and go through defrost cycles to manage frost on the outdoor unit.

Why does my heat pump click so often when it’s cold outside?

Clicking is usually caused by relays and reversing valves switching during startup, shutdown, or defrost cycles. This is common during cold Massachusetts weather.

Should I turn my heat pump off if it’s making noise?

No, not unless the noise is loud, continuous, or paired with a loss of heating. Turning the system off can actually make comfort issues worse during cold weather.

Can a heat pump noise mean it’s about to fail?

Most noises do not indicate failure. Grinding, screeching, or loud banging sounds should be checked immediately, but clicking, buzzing, and hissing are usually normal.