Responding back to my question I posted Sept 27, 2012 (2008 G37 Coupe Raddle or Knock Sound)

Responding back to the question I posted September 27, 2012 regarding to the 2008 G37 coupe raddle or knock coming from under the car. The Infiniti dealership so called pinpoint the sound coming from under the car, and it was the heat shield. The Infiniti dealership removed the heat shields, and keeps my car for a week to do test drives so to see if still will raddle or knock. After having the car for a week, the dealership said they fixed the problem with the knock or raddle sound, and gave my car back to me. Within 30 minutes after I pick up the car, I stop at a red light the raddle or knock coming from under the car appear again. Worst case scenario could this be the catalytic converter and is this cover if I have warranty. Can someone help me because I need know what the problem is because Infiniti is having a hard time finding out the problem? And FYI my car just passed the emissions test two weeks ago (Late Sept 2012) but I been hearing the raddle or knock sound since June 2012.