I just recently bought a 2009 g37 sedan with 120,000 miles runs perfectly no check engine lights transmission smooth car sounds great. The only problem is that the car has a weird rattle from under the car sounds like it’s coming from one or both cats. I was driving and outta no where the car didn’t wanna go over 40mph when I would try to go over 40mph the car would jerk but no check engine light. While this was happening the rattle got louder. The next day I drove it for a bit and drove normal. Could this have been caused by bad/clogged cats??

 

There's a known issue with the passenger cat failing. I'd replace it with high flow cats or test pipes/long headers.