Crackling sound from Rear end area

[@kosikojak]

I have a 2007 Sports trac, 4.0 V6, AT, 36K miles, and when taking off from a stop I hear a crackling sound on takeoff roll (about 8 times out of 10), as soon as I start moving the sound goes away. Sometimes also when shifting in to drive from either park or reverse will hear the same sound once the transmission goes into gear, but thats only 3 to 4 times out of 10 and again once I'm rolling no sound, only on initial takeoff roll do I hear the sound. If i'm rolling at a slow speed then speed up the sound is not there. The crackling sound seems to be coming from the Rear end only and recently had the xfer case fluid swap and the auto transmission complete fluid exchange done at the dealer(I did this for scheduled mx not for the problem), the crackling sound was there before the fluid swaps were performed and had no impact on the sound after completion. I looked at the driveline and rear end for anything obvious and saw nothing. Any areas I should start first easiest to hardest? Could this be possibly suspension related?

V/R
Thanks.