What does an AC compressor sound like when it's going out?

When an air conditioning compressor is failing and nearing the end of its operational life, it typically produces several distinct and concerning acoustic warning signs. One of the most common sounds is a loud, persistent metallic rattling, clicking, or clanking noise, which often indicates that internal components like valves, pistons, or connecting rods have broken loose or suffered severe mechanical wear. Another frequent symptom is an unusually high-pitched squealing or screaming sound, which points toward severe friction from failing internal bearings or extreme pressure buildup within the system. You might also hear a deep, heavy buzzing or humming sound accompanied by a clicking noise from the contactor; this often happens when the compressor is trying to start but fails due to a locked rotor condition, meaning the internal motor has seized up completely and cannot spin. These unusual noises are clear indicators that the compressor requires immediate professional diagnosis before it trips breakers or suffers a complete burnout.