I have a 00' GT with about 48,000 miles. A couple of months ago my car started sputtering/missing, so I went to autozone to have some codes pulled, which indicated a bad o2 sensor (didnt know at the time). I cleaned my mass air and changed spark plugs but still had the problem, and a rich and lean condition. Now for my question. Well, a couple of weeks ago my car started making a metal ticking sound. I thought it might be an exhaust leak, but it really doesnt sound like one. Could the engine be damaged from the bad o2? The only thing that gives me a little hope that my cars not gonna blow up is it doesnt make the sound when the engine is cold, only after its been ran. It constantly ticks at idle, and the sound speeds up with the engine, its almost like a rattling sound. I have no idea what it is or what to do, and i dont want to cause any more damage than there already may be. Any help would be appreciated. Feel free to ask any questions, I know my explanation of the sound might not be very helpful.