My car has done 135 K. While driving in the second or thrsd gear with low RPM i can hear the rear differtial voice, whereas if i accelearte the engine and the car goes in the high speed then there is no voice at all.

Is there anything which can be taken care off, like changing the differtial oil or any special lubricant which should be mixed with the existing oil in the differtial so that the slight noise coming in low RPM could go away.

Any suggestions will be highly apprecaited. Over all the car is in great form...