I'm not sure if you have wheel spacers or not but mine made a poping noise. I know it sounds crazy but all of a sudden one day, my front end started making this pop sound with a slight vibration and it got louder with speed. Put it on the lift at the local shop an dinitially we thought it was the t case. But we went with the simplest thing first. We impacted the spacers down as tight as we could. after a test drive, the pop sound and slight vibration it had was gone. Now about every 6 months or so, I impact them again just for good measure.

Another thing to check while you're in your front diff, is the play in the ring and pinion. Hopefully all the hard wheeling you do hasn't wore them any or any of the ring/pinion bearings.