The answer to 'heat exchanger making noise' is that a noisy heat exchanger is usually caused by a problem with the internal components of the heat exchanger. Common causes include a cracked or damaged heat exchanger, loose internal components, or buildup of debris and dirt. Symptoms may include unusual banging, rattling, or humming noises coming from the furnace or air handler.
In many cases, a noisy heat exchanger indicates a more serious underlying issue that requires professional repair or replacement. Attempting to DIY repair a heat exchanger is not recommended, as it can be dangerous if done incorrectly. It's best to call an HVAC technician to properly diagnose and fix the problem to ensure safe and efficient operation of your heating system.