Furnace making noise? What each sound can suggest

A loose access panel or register can create a harmless rattle, while a squeal may come from a blower belt or motor bearing. A delayed boom at ignition is not a normal furnace sound and deserves prompt attention because it can indicate ignition or burner trouble. Scraping, grinding, or a new vibration can point to blower or wheel damage. Turn the system off if you smell gas, hear a harsh electrical buzz, or see smoke. Do not lubricate a motor unless the equipment instructions specifically allow it. Record when the sound occurs, whether the heat output changes, and how old the furnace is. Those details help separate a repair from replacement.