The answer to 'heat exchanger making loud noise' is that a malfunctioning or damaged heat exchanger is the most common cause. This can be due to cracks, corrosion, or other wear and tear that allows the heat exchanger to vibrate or rattle during operation. This is a serious issue that requires prompt attention, as a damaged heat exchanger can lead to carbon monoxide leaks, which pose a major safety hazard.
If you hear loud noises coming from your furnace's heat exchanger, it's important to shut off the system immediately and call a professional HVAC technician. Attempting to inspect or repair the heat exchanger yourself can be extremely dangerous and is not recommended for homeowners. An experienced technician will be able to properly diagnose the issue and recommend the best course of action, which may involve repairing or replacing the heat exchanger.