Roy Reardan

Hi I'm Roy I have a 2000 Jeep Grand Cherokee LTD 4.7L Not sure if it is a wj or how you even find that out and that is why I'm here. Have had some problems with the Jeep and was looking for advice, I had this howl in the rear end and took it in to find out what it was, they pulled the cover off and found some iron filings and two pieces of metal that looked like two quarters, flat and round about the same size as a quarter. Anyways the howl is gone and they didn't fined any gears that were damaged or any thing else for that matter so they cleaned it out added new oil and put everything back together, it has no more howl and seems fine. Any suggestions would be great.
Please be patient with me as I'm trying to learn this site, not sure if this is to go here or not, please forgive me if this is the wrong place.