Reasons Behind Strange AC Noises

As top AC repair specialists in Alabama, we at AirNow Cooling & Heating get a lot of questions about noises coming from the AC system. Any abnormal sound beyond the standard whooshing of air tends to worry homeowners, and indeed, some of these could signal a problem in your HVAC system. 

What do various noises mean, though? Here is a basic primer for what certain sounds might signal, and what you should do.  


Rattling is one of the more straightforward sounds you might hear – if something sounds like it’s loose in the AC system, it probably is. The trick is just finding what and where, which can be difficult in some cases. If you have any doubts about your ability to search safely here, call our pros.  

Squeaking or Thumping During Startup 

Generally due to worn belts or other moving parts, you will most likely hear squeaking noises either during startup or shutdown of the system. These are the sorts of issues that are generally prevented by yearly heating and air maintenance, however.  

Popping or Puckering 

There’s a significant amount of metal involved in your AC system, and metal is known to expand and contract based on changes in temperature. As such, it’s possible for your ductwork to make a popping, clanging or puckering noise. This isn’t actually damaging to the system itself, but if the noise bothers you, consider insulation or foam to decrease it.  

Clanking or Scraping 

This is another possible signal of loose parts, including possibly fan blades that fall out of alignment. It may also mean pipes are hitting other parts.  


Hissing is a telltale sign that air is escaping from the system, which can cause you major cost issues. In some cases this is due to vent flaps that are closed too tightly, or in others it might be due to a filter that isn’t sealed well.  


In most cases, a bubbling noise means air is trapped in the refrigerant line, usually due to a refrigerant leak. This is a case where you need to call one of our HVAC pros right away. 

For more on common explanations for the sounds your AC might make, or to learn about any of our heating and air servicesspeak to the pros at AirNow Cooling & Heating today.