The recommended gear oil for your car is 75W-85. Mechanics love to pour thick gear oil like PSO 140 but that is not for this car.
If you're using the wrong gear oil, then by pouring in right gear oil, the noise at morning will vanish.
But I am sorry to tell you that if your gear box has developed a noise on acceleration, which is locally called as "goonj", it will never go away by gear oil change. With the passage of time, the teeth of the gears undergo wear and tear, specially if the car is driven without proper gear oil or abused at high RPMs as a routine.
I have experienced the exact same thing with my Khyber. A noise on acceleration which goes away when you release the accelerator. Its gear shifter seal leaked a couple of times and there were periods during which the car was driven with very less gear oil. So it developed that goonj sound. I consulted the issue with half a dozen mechanics and machinists and all said that it can never go away as in such cases the polish on gear teeth is finished. The only option is to change the gear box. My mechanic was persistent that I should pour in a thick gear oil as as he believed that it will lessen the noise. Although I never deviate from owner's manual but as a last try I went on with his idea. Wasted Rs. 1000/- The noise did not reduce. In the end I have to replace the gear box with a kabuli one. It was in very good condition. Now using ZIC 75W-80 oil in it. Going good.