2003 edge 3.0 5 speed 2wd

just noticed yesterday since radio was off a faint whine from 25 or 30mph down to a stop. it's faint and sounds exactly like the howl you hear when on the highway. if the radios on you won't hear it. or wind noise will block it out too, so you have an idea of how loud it is. some history, I did the pinion seal on this maybe 3000 miles ago and did the "mark everything and line it back up" instead of properly putting in a new crush sleeve and all that, which I dunno how to do. not sure if this is related or not. no high speed noise, groan, whine or anything.


any idea where to start? deffinetly sounds engine or trans related, as I can put the trans in neutral and coast, it still does this.

 

Then noise would be drive line or differential, and differential would be my guess

 

looks like there's a few different choices for differentials when buying parts 7.5, 8,8, or a few dana choices. how do I find out which one I have in my truck