The answer to 'humidifier making loud noise' is that there are several common causes, including a buildup of mineral deposits, a problem with the humidifier motor, or an issue with the water supply. Loud noises from a humidifier can indicate that it needs maintenance or repair.
If your humidifier is making loud noises, first check for any mineral buildup or debris in the unit. You may be able to clean this out yourself, following the manufacturer's instructions. However, if the noise is coming from the motor or you're unsure of the cause, it's best to call in a professional HVAC technician to diagnose and repair the issue.