I've only owned my 06 KJ for a few months so I don't know if this is normal or not. After driving, when I'm parked, I hear a pinging, crackling noise like metal cooling. Sounds like it's coming from the back somewhere, not sure exactly where. Is this normal cooling/settling noise or should I have it checked out?

Normal exhaust noises,just think at full operating temps your cats are at or above 1200 degrees inside.

sounds like metal going through its heat cycle, muffler, pipe, cat, shield somewhere...