The answer to 'air handler making noise' is that there are several common causes, including worn bearings, loose components, or a problem with the blower motor. Symptoms may include grinding, squealing, or rattling noises coming from the air handler unit. The solution often depends on the specific cause, but can range from tightening loose parts to replacing worn components.
In many cases, it's best to call in a professional HVAC technician to diagnose and repair the issue, as they have the expertise and tools to properly identify and fix the problem. However, for minor issues like loose screws or debris buildup, a homeowner may be able to address the problem themselves with some basic troubleshooting and maintenance.