[CREWZIN]

Welcome to the forum. Advise......get your PT and run/drive as far away from that crook....errr, I mean dealer as fast as you can. You've been ripped off and he's trying to do it again with the 02 sensor. Luckaly you had the extended warranty and didn't pay too much.

Take it to almost any decent auto shop (Goodyear, Firestone etc.) and tell them to replace the 02 sensor that by the CAT, or do it yourself for a fraction of what that dealer wanted for it.

Noise is hard to diagnose over the internet but the 02 sensor shouldn't be the reason for it. It could be a faulty or malfunctioning IAC (Idle Air Controller) which would make the engine rev oddly but that's only a guess. Ask around and find a trust worthy mechanic.