So I'm asking for my girlfriend, she's taken it to a few shops and no one can give her an answer.
She has a 94 honda accord and it makes this rather loud knocking sound when she lets off the gas, I've only ever heard it when she's driving interstate speeds. Sounds like its underneath in the middle of the car, she told me it never did this till after the catalytic converter was replaced.
Any ideas?

 

vid plz