Hopefully some good information to help others narrow down issues:

So I had two noises going on at once, one ended up being because of bad baffles in the exhaust system, the other was a metal on metal noise at all times, kind of like brake pads engaged to the rotors at all times. Was worried it would be the differential, or other expensive part, but it wound up being just that, brake pads.

The pads of the brake shoe or parking brake that is. The LR tech I use was well aware of what it could be from past experience on some RR sports and LR3/4. The pad material actually delaminates from the shoe itself because of the glue/epoxy failing causing it to hang inside the rear rotor, and thus grind on the inside of the rotor.

Mine had actually worn down the inside of the rear rotor enough for it to need replacement even though the main rotor material was thick enough for regular brake use. So some new rotors and parking brake shoes/pads are on their way, hopefully solving the problem.

Hopefully this can be of use to others troubleshooting grinding/metal noises
!

 

Exact same thing happened to me a few years go; however, it happened right after (and as a result of) a bad EPB adjustment by the dealer service dept. I got all new stuff for free, covered by their own parts/labor warranty.

 

Seems line a warranty issue if you are still in the time frame. If the parking brakes are like other vehicles, they are actually "drum" brakes in the I side of the rear rotor. That means replacement involves tearing apart your entire rear brake system including rotors.

 

Unfortunately no, over 100k miles on an '06. 4th owner.