Moan at between 35-40 MPH

I dunno I just went for a drive again and now it seems to happen all over the range of speed. It also seemed to get louder going into the throttle, and softer coming out of it, but sometimes not. When it is moaning it doesn't always matter whether I am on the throttle at all, it will still do it just coasting, decelerating, or anything. Anyhow, I think I need to take more notes and define the issue better. It may be just something to live with until I actually open the rear up and do something about it. If it were a driveline angle issue I would assume I would get some kind of vibes and not a moan.