The answer to 'why is my thermostat making loud noise' is that the thermostat may have a faulty or damaged internal component that is causing it to make a loud noise. This could be due to issues with the fan, compressor, or other internal mechanisms within the thermostat.
Some common causes of a noisy thermostat include a failing fan motor, a loose or worn-out component, or a problem with the internal wiring. The noise may be a buzzing, clicking, or grinding sound, and it may get louder or more frequent over time. If the noise is persistent or getting worse, it's best to have a professional HVAC technician inspect and diagnose the issue.