When I start the vehicle and drive in slow speed I can hear a whining

Noises are the most elusive of creatures, bangs and grinds are usually much worse things to hear than whines and hums, Every driver gets used to the way their car feels and sounds and if you know that you are hearing something different then there is a problem starting. Check the obvious things like the colour.smell and level of the tranny fluid. I can't imagine you are into something major at 70000 miles and to be honest your mechanic probably isn't hearing anything because he didn't drive your car for 70000 miles on a daily basis. Keep your ears open and watch for any signs of eratic responses in driving but until it becomes more than a whine that only you recognize as being differest you are not going to get a diagnosis.(just being honest)

meant different (not differest)