What cause of constant sound of exhaust manifold?

A constant sound from the exhaust manifold can be caused by a leak, often due to a crack in the manifold or a failed gasket. This leak allows exhaust gases to escape before they reach the rest of the exhaust system, creating a loud, hissing, or popping noise. Other potential causes include loose or damaged mounting bolts or heat shield issues. Diagnosing the exact source typically requires a visual inspection or listening for the sound while the engine is running.