Just bought the car at 144k miles now I’m on about 147k and starting to find some issues hear rattle when I accelerate some times not sure what it is also starting to hear a whine to not sure if it connects the p0420 code which is cats I’m 17 not super mechanical need help

 

So I literally had this problem last year. It’s your cat. Could be one,could be both. That you have to figure out. The honeycomb structure inside the cat has broken apart. It’s the pieces inside that you hear rattling. Also the reason for the code you’re getting. The dealer wanted $800 for (1) cat. I bought Berk hfc for 550ish. Put em on. It cleared the code,no more rattling and gave me some performance.