2004 CHEV TAHOE LS. Rattling noise front of vehicle. follows engine rotation.

What is your question?

All engine parameters okay. No over heating, Oil okay. Water temp ok. No leaks. Radiator fan not rubbing. No reduced performance. etc. Noise occurred for two wks then code P0420 appeared, bad O2 sensor? When driving 20mph + no noise (?)(probably can't hear), then at idle rattling again with rotation. Miles 106000, been a really good vehicle. How is a defective Catalytic converter related to following engine rotation?

What makes this problem better or worse?

Better or not there at higher highway speeds

How long has your 2004 Chevrolet Tahoe had this problem?

2-3 wks