Cummins engine noises like combustion knock, valve train tick, and bearing squeal signal underlying issues. Diagnose via checks on fuel quality, compression, valve lash, and accessories. Fixes include decarbonization, timing calibration, lash adjustment, and component replacement. Proactive maintenance (cooling system care, proper break-in) prevents failures. Persistent noises may indicate serious damage; use tools like INSITE™ or seek professionals.