The answer to 'why is my evaporator coil making loud noise' is that a noisy evaporator coil is often caused by a problem with the fan motor or blower. This could be due to a worn-out bearing, a loose fan blade, or debris buildup. A loud evaporator coil can also be a sign of a refrigerant leak, which can cause the coil to freeze up and make noise as the ice melts and refreezes.
If the noise is coming from the evaporator coil, it's best to have a professional HVAC technician inspect and diagnose the issue. Attempting to repair the evaporator coil yourself can be dangerous and may cause further damage to the system. A qualified technician will be able to identify the root cause of the noise and make the necessary repairs to restore quiet operation.