While your furnace will make some noise as it operates, it shouldn’t make much. You should hear the burners of your furnace (which sound similar to a gas stovetop), as well as the fan, and possibly the electronic ignition (if you don’t have a pilot light). However, you should be wary that other noises can indicate an issue. Keep an ear out for any and all of the following indicators that your furnace is failing:

• Rattling: Rattling can occur in your furnace if a component has come loose. You should have a professional take a look to locate the component and to secure it, before it causes additional damage to your furnace.
• Banging: Banging noises often mean that a component has become completely detached. Again, call a professional right away to take a look.
• Clicking: If you have an electronic ignition, it will click once or twice every time your furnace turns on. However, if you have a bad ignition switch, dirty burners, or restricted gas flow, your igniters may be slow to create a flame. Have an expert take a look at your ignition source. You may need a new ignition switch or another repair.
• Loud bangs: Loud banging is an indication that gas has built up before ignition. Gas can build up and late ignition will cause a small explosion — which is an obvious hazard and may damage your furnace even more. Get help from an HVAC technician, and shut off your furnace and its gas source if you smell gas near the furnace (more on that below).