The answer to 'why is my furnace making loud noise' is that there are several common causes, including worn bearings, loose parts, or a problem with the blower motor. Loud noises from your furnace can indicate an issue that requires attention to prevent further damage or safety concerns.
Worn bearings in the blower motor or inducer motor can cause a high-pitched squealing or grinding noise. Loose screws, panels, or other components may rattle or vibrate, creating a loud, banging sound. Problems with the blower motor itself, such as a failing motor or worn-out fan blades, can also lead to unusual noises from the furnace.