Just ran codes off and came back with misfire on cylinders 2 and 3. Also lean bank 1 codes. I was told to replace O2 sensor wasn't sure if it was front or rear. The car is running louder than usual, and has a rumble for about a min when first starting.

 

It seems that you have an exhaust leak before the front oxygen sensor.Fix the leak and you should be OK.On this model a leak mostly occurs at the manifold where its connected to the head.

 

On my 2001 exhaust manifold the upper nut closest to the driver's side would back off. When first started the car made the classic sewing machine sound from the exhaust leak until it warmed up. I bought a locknut to fix it. Don't use a nylock as the nylon will melt. If you have the same problem then you can reach behind the engine when cold and spin the nut with your fingers. It's fairly easy to tighten.

The misfire codes and lean bank 1 (upper O2 reports this) could very well be related to an exhaust leak. The lean bank 1 is NOT a bad O2 sensor. A failing O2 makes the car run rich. A clogged fuel filter could make the car run lean also. (Assuming you did not put E85 in it as this would definitely run lean)