Strange HVAC Noises Explained | What They Mean in Texas

A buzzing sound from your AC typically indicates an electrical problem. The most common causes are: a failing contactor (relay that powers the compressor), a bad capacitor (stores energy to start motors), loose electrical connections, or a compressor struggling to start. If the buzzing is coming from the outdoor unit and the fan isn't spinning, the capacitor has likely failed. Turn off the system and call for service—running with electrical issues can cause further damage.

A single click at startup and shutdown is normal—that's the relay engaging. However, continuous clicking or rapid repeated clicking indicates a problem. Causes include: a failing thermostat, defective relay, control board malfunction, or compressor trying (and failing) to start. First try replacing your thermostat batteries. If clicking continues, especially if the system doesn't start, you need professional diagnosis.

A low, steady hum during operation is normal—that's the compressor and motors running. However, if the humming is new, louder than usual, or comes without the system actually running, it could indicate: a motor about to fail, a starting capacitor problem, or loose components vibrating. If your outdoor unit hums but the fan doesn't spin, that's a strong indicator of a bad capacitor—a very common failure in Texas heat.

Hissing typically indicates escaping refrigerant (a leak) or air escaping through a duct gap. Check if the sound comes from the refrigerant lines (hissing) or from vents/ductwork (whistling). Whistling from vents often means a dirty filter restricting airflow—replace it first. If the hissing is from the copper lines or outdoor unit, you likely have a refrigerant leak that needs professional repair. Don't ignore hissing from refrigerant lines as performance will decline.

Banging almost always means something loose or broken is hitting during rotation. In the outdoor unit, this could be: a loose or bent fan blade hitting the cage, a broken compressor mount, or debris inside the unit. In the indoor unit, a loose blower wheel or motor mount is common. Turn off the system immediately—the banging part is causing damage with every rotation. This is a repair-urgency situation to prevent cascading damage.

Yes, turn it off immediately. Grinding indicates metal-on-metal contact, typically from: failed motor bearings (most common), a blower wheel rubbing against the housing, or compressor internal damage. Running a grinding system for even a few minutes can destroy a motor that might otherwise be repairable. Turn off the system, note which unit (indoor or outdoor) the grinding comes from, and call for service. Early response can save hundreds in repair costs.

Popping or ticking sounds from ductwork are usually normal thermal expansion—metal ducts expand when warm air flows through and contract when cooling. This is especially common in Texas where temperature swings are significant. However, if popping is very loud or new, it could indicate: undersized ductwork causing pressure issues, ducts striking framing as they expand, or duct sections that are improperly supported. Loud persistent popping warrants inspection.

A squealing or screeching sound typically means belt or bearing problems. In older belt-driven systems, a slipping or worn belt is the likely cause—replace it before it breaks. In direct-drive systems (most modern units), the sound usually indicates motor bearing failure. Squealing that's worse at startup and improves is often a belt; constant squealing points to bearings. Either way, service is needed soon to prevent motor burnout.

Bubbling or gurgling sounds indicate either refrigerant or water issues. If the sound is coming from the refrigerant lines, air has entered the system, usually from a leak—this requires professional repair. If the sound is near the indoor unit, it's more likely condensate drain issues: a clogged drain line can cause water backup and gurgling as air passes through trapped water. Try clearing the drain line with a wet-dry vacuum first.

Costs vary significantly by cause. Simple fixes: loose panel ($0 DIY), dirty filter ($5-25 DIY). Common repairs: capacitor ($150-350), contactor ($150-300), blower motor ($400-900), fan motor ($300-600). Major repairs: control board ($400-800), compressor ($1,500-3,000+). Diagnostic fees in North Texas typically run $89-150, often credited toward repairs. The key is addressing noises early—a $200 motor bearing repair becomes an $800 motor replacement if ignored.

Call immediately for: any sound accompanied by burning smell or smoke (turn off at breaker first), loud bangs or explosions, grinding or shrieking sounds (turn off immediately), continuous electrical arcing or popping, or any noise combined with the system not cooling and vulnerable people in the home. After-hours emergency service typically adds $150-250 to the bill, but some sounds indicate damage that worsens by the minute.

You can narrow down the issue by: locating the source (indoor unit, outdoor unit, or ductwork), noting when it occurs (startup, running, or shutdown), checking if it correlates with performance issues, and recording the sound on your phone. Safe DIY checks include: replacing the filter, checking for debris in outdoor unit (visually, don't open it), tightening loose cabinet panels, and clearing the condensate drain. Never open electrical panels or touch capacitors—they hold dangerous charges even when power is off.