rear differential problems.....what else can i do
 

i have 04/4.6/2wd/76,000 miles

about a month ago i notice a dragging/thumping noise coming from the rear end when taking corners/turns. i have had the rear differential drained and cleaned . i have added the ford friction additive also along with fluids. the vehicle still has problem. going forward and reverse is no problem. anyone have any suggestions would be appreciated

by the way it only does this once vehicle is warmed up or normal driving conditions