The answer to 'furnace making loud noise' is that there are several common causes, including worn bearings, loose parts, or a problem with the blower motor. Symptoms may include banging, rattling, or screeching noises coming from the furnace. Some solutions, depending on the cause, could be replacing worn parts, tightening loose components, or repairing or replacing the blower motor.
In many cases, it's best to call a professional HVAC technician to diagnose and repair the issue, as they have the expertise and tools to properly identify and fix the problem. Attempting DIY furnace repairs can be dangerous if you're not trained, and may end up causing more damage or safety issues.