When you turn on your air conditioning system for the first time each summer, you may remember how much you love the sound of that gentle whoosh as it kicks on and cools things down. But from time to time, you might hear some other, more troubling sounds coming from your system. Some of them are fairly benign, but others may indicate serious problems. Read on to learn about some of the most common sounds and what they could mean.

  • Rattling: If it sounds like something loose is blowing around inside your system, you’re probably right -- it’s just a question of what and where. Your outdoor condenser is protected by a grate that keeps out large debris, but small things like twigs and pebbles might slip through. Things can also find their way through your indoor vents, especially if they’re installed on the floor. You can usually retrieve these yourself by removing the vent cover, but if you have any doubts about removing the grate on your outdoor condenser, you might want to leave that job to the pros.
  • Clanking or scraping: These metal-on-metal sounds often indicate loose parts, such as fan blades that fall out of alignment and start striking other parts. It could also mean loose pipes are clanking against other parts, which could do additional damage. Call an HVAC specialist to investigate these noises.
  • Squeaking or thumping on startup or shutdown: These noises can easily be caused by worn belts or other moving parts. These components are checked during any thorough tune-up, so consider scheduling one before a worn part becomes a broken one.
  • Hissing: Loud hissing often means air is escaping where it shouldn’t. If the sound is coming from inside your walls, it could indicate leaky ductwork. If it’s coming from your vents themselves, your vent flaps might be too tightly closed. You might even hear this sound coming from the area of your filter if the filter doesn’t form an adequate seal.
  • Metallic popping or puckering: Because metal contracts and expands with temperature change, your metal ductwork may noisily pop open or clang shut. This isn’t harmful to your system, but you can use insulation or foam to cut down on the excess noise.
  • Bubbling: A bubbling sound often suggests that air is trapped in the refrigerant line, possibly caused by a refrigerant leak. Call an HVAC technician right away if you hear this one -- it can cause extensive problems.

If you’ve noticed unusual sounds emanating from your HVAC system, you don’t have to diagnose them on your own. Just contact your local technicians and get some expert help quieting things down again.