Rattle

Just recently noticed this rattle that only happens during idle. Doesn’t respond to clutch engagement, seems to be louder under the truck than in the engine bay. I held/pressed on the cat and exhaust. Doesn’t seem to be loose and made no change to the rattle.

 

I recently replaced my rear main seal, I had to fill the transmission back up due to loss from the hardlines. I added a quart and the rattle that I've had for 2 years is gone. I would say low transmission fluid is the culprit

 

There should be a heat shield on your exhaust. Check that it is tight. Also check to see if any rocks have gotten up in there.