A loud buzzing or whining when the transmission is in reverse may be caused by a regulator valve in the transmission valve body. A revised valve was released that does not resonate. Careful diagnosis should be performed because other causes can create the noise.
Car Problem Reports
Dodge Ram 2500 Regulator valve may cause noise when transmission is in reverse
Dodge Ram 2500 Problem
Drive Trains Affected: 4WD, Automatic Transmission