Light rattling when accelerating.

I bought a used 2006 prius a couple years ago. The previous owner said the cat was stolen before, they had it replaced, and installed a cat shield.

There is a consistent rattle during acceleration only when the gas engine kicks in. When idle or coasting there is no rattle. Im usually very light footed, but if i have to climb up a hill or speed up quickly, the rattle becomes much louder and more prevelant. Its always a consistent rattle, and during acceleration.

The seller said the rattling is caused by the catalytic converter hitting the shield, and I took it to a mechanic who said it was fine. It passed smog check no problem.

Online searches said there could be a bunch of reasons including breaks, clogged catalytic converter, engine gasket, spark plugs and etc.. Does anyone know where it's really from?


Thank you.