Now I think the shield on my 1st cat converter is vibrating. It is REALLY apparent when in the garage and the sound reflects off the walls. It sounds very strange, not a typical heat shield rattling sound, but rather sounds like ticking, just like the injectors! The sound is definitely coming from the cat converter as I had my ear right next to it.

The sound only happens at idle in "Drive" and on the brake pedal. It goes away at any other RPM so this leads me to believe it's a vibration noise. I tried holding the hot heat shield with a mop but it did nothing, as if the sound is coming from inside.

Any ideas?

 

Well I shot it twice with my rifle and it's still making noise