Where is my axle noise from?

Just pulled my 7 1/4 drums and axles out and the bearings seem ok. Driving down the road I hear a pretty good hum. It does not change with acceleration or deceleration. I'm wondering now if it's the spider gears? The other 2 A body cars I have are sure grip. So I don't have a good way of comparing. Does this look / sound normal? Diff lube is up to the mark and smells ok. [ame="http://youtu.be/bNPzGPLpGyY"]http://youtu.be/bNPzGPLpGyY[/ame]