Burning oil and making a noise.

I bought a used 02 accord. It ended up having a seriously plugged cat. I put on headers and a test pipe last night. It has been idling rough randomly since I got it. I was told by the mechanic that looked at it that it was the cat causing it. Now that I put those on I can hear a whiring sound from the engine towards the pulley end of the motor. It is consuming a quart a week, but I have been using 5 20. I am going to switch to 1030. It doesn't seem to smoke constantly, but when its idling rough it pours out. What's the most likely cause? Rings or valve seals? Noise sounds kinda like a weed eater when revving but not through all rpms. I am assuming the noise was there but not audible through the thick manifold. What are the chances an engine cleaner will help? How hard is it to do the rings and do I have to have the cylinders machined or can I just drop the bottom end out? Im good at turning a wrench but lack diagnostic skills.