The answer to 'ductless system making loud noise' is that a noisy ductless HVAC system can be caused by a variety of issues, including a problem with the compressor, fan, refrigerant levels, or loose components. Common symptoms include grinding, rattling, or whistling sounds that may increase in volume over time.
Some potential solutions include tightening loose screws or panels, cleaning the outdoor unit, and checking refrigerant levels. However, if the noise persists or worsens, it's best to call a professional HVAC technician to diagnose and repair the issue. Attempting to fix a complex ductless system on your own can be dangerous and may void the warranty.