What does the knocking sound like on bad catilick converter?

A knocking sound from a bad catalytic converter often resembles a rattling or metallic clanging noise, especially when accelerating or idling. This sound can occur due to internal components, such as the catalyst substrate, breaking loose or becoming damaged. Additionally, if the converter is clogged, it may produce a more pronounced thumping sound as exhaust gases struggle to pass through. Overall, any unusual noise from the catalytic converter warrants immediate inspection to avoid further engine damage.