Every air conditioner makes some noise. A steady whoosh of air, a low hum from the outdoor unit, one soft click when it kicks on — that’s a healthy system. What matters is a new sound, or one that keeps getting louder. Air conditioners are pretty good at telling you what’s wrong before they quit, and the sound they make usually narrows it down to one or two parts.
Here’s how to read what you’re hearing, and how fast you need to act.
Shut it off first if you hear any of these
Some noises mean “keep an eye on it.” These mean “stop the system now”:
- Screeching or a high-pitched squeal that wasn’t there before
- Loud banging, clanking, or grinding from the outdoor unit or the blower
- An electrical buzz combined with a burning or hot-plastic smell
- Any noise paired with a rotten-egg smell — that’s a possible gas leak; leave the house and call your gas utility or 911 from outside
Turn the thermostat off, and if the noise is coming from the outdoor unit, shut it off at the breaker too. Almost every expensive HVAC failure starts as a cheap one that somebody ran for another three weeks.
What each AC noise means
| Noise | What it sounds like | Likely cause | Urgency |
|---|---|---|---|
| Screeching / squealing | High-pitched metal-on-metal or a sharp whistle | Failing blower or fan motor bearings; worn belt on older units; in rare cases dangerously high compressor pressure | Shut off now — call same day |
| Banging / clanking | Heavy thud or metallic clank, often rhythmic | Loose or broken compressor component, unbalanced blower wheel, loose mounting hardware | Shut off now — call same day |
| Grinding | Rough, dry, metal-grinding drag | Motor bearings failing without lubrication | Shut off now — call same day |
| Clicking | Repeated rapid clicking at startup, or clicking that never stops | Failing capacitor, contactor, or relay. One click at start and one at shutdown is normal | Call within a few days |
| Buzzing / humming | Electrical hum from the outdoor unit, often with the fan not spinning | Failed run capacitor, loose wiring, chattering contactor, or debris jamming the fan blade | Shut off, call promptly |
| Rattling | Loose, shaky vibration that rises with fan speed | Loose screws or access panels, gravel and debris inside the outdoor unit, dirty blower wheel, unsupported duct | Check clearance yourself; call if it persists |
| Hissing | Steady air or gas escaping | Refrigerant leak, leaking duct connection, or a pressure valve. Brief hiss at shutdown is normal | Call within days — sooner if cooling is weak |
| Gurgling / bubbling | Water glugging through a line | Partially clogged condensate drain line; occasionally refrigerant moving through a low charge | Call soon — water damage risk |
| Booming / rumble on the heating side | A delayed whump when the gas furnace lights | Delayed ignition from dirty burners — a combustion safety issue | Shut off now — call same day |
The noises that mean stop running it
Screeching, squealing, and grinding
These are almost always bearings. Blower motors and outdoor fan motors ride on bearings, and once those dry out or wear, metal starts riding on metal. Caught early, it’s a motor replacement. Ignored, the motor seizes, and on some systems that takes the fan blade or the blower housing with it. A worn belt on an older air handler makes a similar squeal, and that one is cheap — but you can’t tell them apart by ear from your living room.
There’s one more possibility worth naming: a loud, sustained scream from the outdoor unit can indicate dangerously high pressure inside the compressor. That’s rare, but it’s a real reason not to “just let it finish the cycle.”
Banging and clanking
A rhythmic bang usually means something is loose and moving where it shouldn’t. Inside the outdoor unit that’s often a compressor mount or an internal component that’s broken free. On the indoor side, it’s typically a blower wheel that’s out of balance — sometimes because a chunk of built-up dust broke off one side. Either way the system is beating itself up every minute it runs.
Buzzing with no fan movement
This is the single most common summer emergency call in El Paso, and it’s usually the cheapest one to fix. The run capacitor is the part that gives motors the jolt they need to start turning. When it fails, the motor gets power but never spins — so you get a hum and no air. Heat kills capacitors, and a July afternoon in the Upper Valley is exactly the condition that finishes off a marginal one. Shut the unit off. A humming motor that can’t turn is pulling heavy current and cooking its own windings.
The noises you can often trace yourself
Rattling is worth two minutes of your own time before you call. Kill the power at the disconnect or breaker, then look at the outdoor unit: dust storms push gravel, tumbleweed fragments, and dead leaves through the coil fins, and a single rock bouncing around the fan cage sounds alarming. Check that the access panel screws are tight and that nothing is leaning against the cabinet. Keep two feet of clearance on all sides.
Gurgling almost always comes back to the condensate drain. Your evaporator coil pulls humidity out of the air — a lot of it during monsoon season — and that water leaves through a small drain line. Dust and algae narrow it, water backs up, and you hear it glugging. Left alone it overflows the drain pan, which is how ceiling stains start. This is a standard AC repair visit, not a major job.
Popping and booming in the ductwork is sheet metal flexing when pressure changes. It’s louder in homes where the duct was never resized after a swamp-cooler conversion, or where too many registers have been closed off. Correcting it is a ductwork question, not a repair — but it’s also telling you the system is straining for airflow.
Why El Paso systems get loud
Three local conditions do most of the damage here. Dust and blowing sand pack coil fins and get into bearings, and that grit is what turns a quiet motor into a screeching one. Extreme heat load means compressors and capacitors run at the edge of their rating for four months a year. And a lot of homes on this side of the valley are running older equipment or a conversion from a swamp cooler, where the air handler is newer than the ductwork attached to it — that mismatch shows up as vibration, whistling registers, and duct booming.
None of that is fixable by turning the volume down. It’s fixable by keeping the coils clean and the filter fresh, and by catching the worn part while it’s still just a noise. A yearly maintenance visit before summer catches bad capacitors, loose blower wheels, and dry bearings when they’re a small line item.
When noise means it’s time to replace
If a system is 15 or more years old and the noise traces back to the compressor, the math changes. Compressor replacement on an aging unit often costs a meaningful share of a new system that will use far less electricity — ENERGY STAR’s guidance on aging equipment is worth reading before committing to a big repair. We’ll tell you plainly which side of that line you’re on, and we’ll quote both so you can decide. Straight answers cost nothing.
Israel Sheet Metal has been a family-owned, licensed HVAC and sheet metal company since 1992, serving El Paso, Canutillo, and Las Cruces. If your AC is making a noise it didn’t make last summer, shut it off and call us at (915) 877-2284 — same-day service Monday through Friday, and a free quote on any repair or replacement.