My car makes a whining noise when I press on the.

My car makes a whining noise when I press on the gas. Although It will still runs smoothly with no hesitation. No jerking. Or stopping. I notice the noise after I had my transmission fluid flush and drained. When I got it diagnose with manufacturer they said I have a bad differential bearing on my transmission and recommend replacing the whole transmission which will cost me 3,000K. Too much to pay. Would like advice to find out if you can figure what causes the whining noise.I thinking this problem was cause by the dealership, but they won't admit to it.