OK. I've always heard a small rattle at idle & it has been bothering me for a few yrs. I fugured out today that it is some sort of ring on the O2 sensor. Anyone else have this problem?? Can't figure out how to fix it. Suggestions?

 

If your O2 sensor has a washer (ring) installed, then your O2 sensor needs to be tightened down until the washer is fully seated. O2 sensors can be tight fits; it helps to have the exhaust warmed up (don't burn yourself) and you may need an O2 socket (about $10 from any auto store) to get to it.