Why is my AC making a strange noise?

Different noises indicate different problems. Squealing or screeching often means a worn belt or motor bearing. Banging or clanking suggests loose or broken internal parts. Hissing could indicate a refrigerant leak. Clicking may be a failing compressor or relay. Rattling can be loose panels or debris in the outdoor unit. Any unusual noise that persists should be inspected by an HVAC professional to prevent further damage.