A transmission whine noise can be an indicator that the transmission components (bearings or gears) are not rotating correctly. It is possible they are worn out or damaged. This is just a suggestion, not a diagnosis.
I suggest you take the vehicle in for an inspection. A certified technician will be able to offer an accurate diagnosis after a physical inspection.
This is an issue that you will want to take care of sooner than later, as to avoid more costly repair in the future.
I hope this information is helpful.
If have you have additional questions, please feel free to contact me.
GM Customer Service