The answer to 'why is my mini split making loud noise' is that there are several common causes, including a malfunctioning compressor, loose parts, refrigerant leaks, or issues with the indoor or outdoor fan motors. Loud noises can indicate a serious problem that requires professional diagnosis and repair.
If your mini split is making a loud banging, rattling, or grinding noise, it's best to shut it off and call an HVAC technician right away. Continuing to run the system could lead to further damage and more expensive repairs. The technician will be able to identify the root cause of the noise and recommend the appropriate solution, whether that's a part replacement, refrigerant recharge, or other repair.