Need Help - Grinding Noise After Rear Diff Fluid Change

[BLUE SQUARE]

Okay Gents,

I am in the process of installing my flip kit and C-Notch and my bed is off. I figured this was the time to freshin things up, so I changed the oil in the diff.
I took the cover off and replaced the gasket on my 10 bolt rear end, and now I hear an occasionaly grinding. I put synthetic lucus gear oil in it. Has anybody ran into this issue. I was backing out of my drive way when I heard it. It sounds like a osilating grind every 10 revolutions or so. I may take it appart to inspect. but, I wanted to see if anybody has experienced this issue. I appreciate any advice you guys can give me. I don't want to damage anything. Thank you.