Rotating thudding sound while decelerating
 

OK...need some help here from the experts.
I notice a low thudding sounds while off the throttle and decelerating, usually at speeds above 25MPH. Most noticeable going down long hills. It sounds almost like a tire out of balance or a wheel bearing type sound. If I out it into neutral, the sound goes away.
More info:
06, almost 100k, previous owner did all dealer service.
Not tires: New tires just went on. Same before and after.
Both front complete control arms were put on when I bought it.
Alignment done when I bought it.
It is not louder while turning.
Nothing heard while cruising with throttle applied.
Transmission shifts perfect.
High/Low range works perfect, all diffs lock as should (was just off road last weekend going to a hunting/ski lodge...mud, snow and even pulled my friends Silvarado out of the mud). Used all programs. Has rear locker and it engaged a few times.
Sound seems like it is coming from the front but hard to tell.
Tried to take video/audio but it isn't audible on the recording. It is not super loud, but I hear it.
Any thoughts on this? Have a few longer ski trips coming up so want to see if there might be something to address.

Does it worsen when applying the brakes?