but that is ruled out because if you let off the gas or shift to neutral at 40-50 mph it doesnt do it, so if your still traveling the same speed then it should make the noise no matter what.
and if you shift to neutral and rev it while still going 40-50 it doesnt make it so i would think that rules out the muffler also. it sure sounds like a muffler with a hole in it but muffler looks good

 

http://www.4crawler.com/4x4/CheapTri...line-101.shtml

Great page with a ton of info on driveline angles.

I had a bad carrier bearing in my 8.25 that made a whining noise under load at higher speeds also, no vibrations or anything just some noise.

 

Nobody has mentioned shackle angle , my jeep was loud inside before I fixed my shackle angle .

 

Oh alright, well that's one more thing ruled out at least.

 

update, pulled the rear drive shaft and its smooth as glass, so it has to be driveline angle.
I don't have the time to mess with it, its going to the shop to get fixed. Damn kids baseball takes up my life right now!