2005 Honda CRV

Noises problem
2005 Honda CRV 4 cyl Front Wheel Drive Automatic 101000 miles

I have a loud rattle under the CRV. I have determined, after speaking to some people, that it may be the heat shield for the catalytic converter. I have a few questions about that. Can it be tightened, or should it be replaced. Does the whole C.C. Need to be replaced? Also, I VERY recently replace my O2 sensor, since the Check Engine Light was on. I'm wondering if it had anything to do with the cat. Conv.? Are they related, I mean, they are both emissions things. I don't' know how those engine codes work, could it be it was mis-read? The CEL came on after gassing up the car and not putting the cap on tight. I found that coincidental that I suddenly had a bad O2 sensor. Anyway, looking for an answer about the heat shield, first and foremost.
July 11, 2010.

Check engine light: Have the computer scanned for code/s-you have a problem within the engine management system that caused the CEL to turn on-This is your starting point of diagnosis, finding out what's going on.

Jul 12, 2010.
The heat shield on honda vehicles will rust and break where the two halves of the shield bolt together. You can get both upper and lower halves and 4 new bolts at your local honda dealer. You do not have to replace cat converter just the shields.

Aug 6, 2010.