w140 tranny whine when off the throttle

[locry]

my dad's w140 S280 tranny has just gotten out of the tranny shop.
The planetary gear assembly needed replacing as a bearing inside the assembly disintegrated, (lost reverse first... went home then this grinding sound started)... resulting in a tranny rebuild... plus a new planetary gear set.
Anyway... everything seems to be running smoothly in all gears... except there's this whine when you let off the throttle... once you apply just a tad of throttle the whine disappears... what could be the problem? will be returning the car tomorrow... just wanted the board's advice as i find people here are much more knowledgeable than most shops here in the Philippines.