The answer to 'why is my ductless system making loud noise' is that there are several common causes, including issues with the compressor, fan, or refrigerant lines. Loud noises can indicate a problem that requires professional diagnosis and repair. Some possible causes include a malfunctioning compressor, worn fan bearings, or a refrigerant leak.
If the noise is persistent or getting worse, it's best to call an HVAC technician to inspect the system and identify the root cause. Trying to repair a ductless system without proper training and equipment can be dangerous and may end up causing more damage. A professional will have the expertise to properly diagnose and fix the issue to restore quiet, efficient operation.