The answer to 'heat exchanger making noise' is that a noisy heat exchanger is often a sign of a problem that requires professional attention. Common causes include a cracked or damaged heat exchanger, loose components, or buildup of debris. Symptoms may include unusual sounds like rattling, banging, or whistling, as well as reduced heating efficiency.
In most cases, it's best to call an HVAC technician to diagnose and repair the issue. Attempting to DIY repairs on a heat exchanger can be dangerous, as it involves working with combustible gases and high-voltage electrical components. An experienced professional will be able to safely inspect the system, identify the root cause, and make the necessary repairs to restore proper and safe operation.