HVAC systems make all kinds of strange noises, even when they kick off. Some of these sounds should raise red flags because they suggest an issue with the system, while others should not. Having a qualified technician inspect your HVAC systems on a regular basis is the easiest way to pinpoint sounds that need attention.

Ductwork Compression and Expansion

In response to temperature changes, the ductwork connected to your HVAC system may make sounds like cracking or popping as it expands and compresses. Dirty or blocked ductwork can also result in strange noises as left-over air tries to squeeze through narrow passages after the HVAC unit kicks off.

Spinning or Damaged Fan Motor

When an HVAC system builds up residual energy, it can cause the fan motor to keep spinning after the system shuts off. This might produce a low humming noise. However, if it produces a shrieking noise, this is a strong indicator that there is damage to the fan motor.

Thermal Expansion and Contraction

When metal parts, like coils, cool down or heat up, they contract or expand, producing a clicking or tapping sound. These noises usually continue for several minutes after the HVAC unit turns off and are not a reason for concern.


If you hear a dripping noise coming from the AC after it shuts off, there’s a good chance it’s water falling from the coils as they cool down. This occurs as a result of condensation. You can minimize condensation and excess leaking from the air conditioner by having a qualified technician wrap the refrigerant lines with proper insulation.

Here at Complete Heating and Cooling, our technicians help people every day in Fredericksburg with their HVAC systems. We also specialize in indoor air quality improvement, indoor humidity control and commercial refrigeration.

Contact Complete Heating and Cooling now if you’re worried about the sound your HVAC system makes when it’s turned off.

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