I've got a few issues going on with my tC right now. The first symptom I noticed was a sound like radio static from under the hood, especially at high rpm. It gets louder after letting off the gas if it is still in gear. This has been getting louder over time. Also, the other day while driving in the rain, my car died and when I got it started again, white smoke was coming out of the exhaust. I know this means water is getting into the engine, but how?

I also have the following codes from AutoZone:

P0138 (O2 sensor high voltage)
P0420 catalyst system efficiency below threshold
P0606 ECM failure

Another common problem is oscillating rpm at idle from 600-800, especially with a cold engine. I thought the exhaust manifold might be cracked somewhere or there is a vacuum leak. Could anyone help?