My car has a knock/rattle when warm. You cannot hear it when it is cold. It seems to be coming from the drivers side of engine near the pan or catalytic converter. No loss of power or codes. I have maintained the car very well. But the noise is quite noticeable when warm.

 

Year, mileage, mods?


Could be a heat shield. Either the ones attached to your cats, or the ones attached to the transmission tunnel above the cats.. I'd get the car in the air and go under there with a flashlight to better pinpoint the exact location with the car warm and running, then do the same with the engine cool and off, that way you can touch stuff and not get burned.

 

2004 with 81k miles and only mods are a cat back exhaust and cold air intake