Teakwo23

Hey guys, I have a 2001 SS. My SES light is on and I know the code is for insufficent cat. I have an SLP Flo Pac and SLP exhaust. Everything else is stock. A trustworthy mechanic that knows F-bodys says he will tune my car for about $300 and get rid of the annoying cat code among a few others I dont need. Will it harm my car to drive it like this? I dont really want to buy a new cat since I want to install long tubes and a ORY in the future. Im also getting a strange noise from underneath the car. Its only after i drive it a few miles and in Drive. It will not do it in any other gear. The sound it makes is like when you ease off/on your brakes and it makes that rubbing sound. Its not a consistant sound. It does it sparringly but you can feel it under the car. The idle is fine and the car runs great. Any suggestions on what it might be? I bought the car private party and it has 59,000 mi on it. Thank you guys!