What is a common sign of a malfunctioning gas furnace?

A common sign of a malfunctioning gas furnace is the presence of unusual noises such as banging or squealing. These sounds can indicate various issues within the furnace. For instance, banging may suggest that there is a loose component or debris in the blower or ductwork, while squealing could indicate that a belt is worn out or that there is a need for lubrication on the motor. These noises signal that the furnace is not operating as it should, and they often point towards mechanical failures or potential safety concerns that need immediate attention. Addressing these sounds promptly can help prevent further damage and ensure the furnace operates efficiently and safely.