What is the whining noise with acceleration caused by?

Well, with such a question as this (no details as to where the sound seems to come from,) there are a couple usual answers for this. If you have a turbo charged (or otherwise forced induction engine), that would be the loudest whine under acceleration. If not, most probably your transmission the gears and other parts of the clutch system will rub together and make a slight whining noise, especially when the motor/transmission is cold. The tranny fluid is more viscous, thus the parts are working that little bit harder to move.