The whine from the back is usually my wife.Then I lube her up..... but thats for another fourm.

 

If it's a pulsating sound you should check your rear wheel pulley bolts to make sure none have come loose and then check your rear rotor to see if it's warped. Do you use your rear brake as your main brake for stopping? If it was your axle/bearings it would be more of a squealing noise after you get the axle heated up with some higher speed riding. If it's not your brake rotor or pulley you should see if you have sufficient antiseize on your rear axle.