I have a 2012 Wrangler 4 door (Diesel) and it deveveloped a rather odd rattling noise on tickover, when driving no noise.
On checking the engine bay I found that the rod that is connected to the engine block and the cat had snapped causing the rattle. I bent the rod and problem solved.

Dealer is order ness parts to repair.

Just a letting all you guys know in case you have a rattle you cant find.
In fact it might be worth checking anyway.