It sounds like carrier bearings to me my car did the same thing,the design of the carrier bearings allows the drive shaft to float to reduce vibration but when the rubber bearing wears out it will allow more movement under torque.If you have the time or get a chance to get under your car grab the drive shaft and shake it you will see alot of movement.The cheap way I have been told to fix this is by injecting hot glue or 3M Windo-Weld Primerless Super Fast Urethane Sealant into the opening at the bottom of the each bearing.I bought new ones after all they were eighteen years old there time had come.