I know this is a an old post but I just want to share my experience. My 2012 Quest had developed a noise coming from the engine bay area 3 months ago which grew louder in a hurry. At first it sounded like a rattling heat shield but soon realized it was an actual exhaust leak.
Long story short I went to my local shop and was told it was the bad soft pipe from the y-pipe with a cat converter. Only OEM replacement was available from where I am (NYC) due to emission standard and it cost well over $1000. While I was sourcing an aftermarket one online I stumbled upon info regarding federal law mandating factory warranty for cat converter up to 8 year/ 80,000 miles. Took the car to a Nissan dealer with 12 miles shy of the 80,000 miles and after a bit wrestling with the service advisor and his manager I got them to replace it free of charge for me.