Noise in from transmission between 40 & 45 mph
 

I have had a humming or whirring noise from my right front under the hood while doing a "soft" accelaration and while holding it between 40 to 45 mph.I took it to the dealership today andI haveto leave it Monday. The mechanic that drove the car today he thought it was the pinion gears on the right side of the trans. I have complained about this for around 12k. Does this make any sense to anyone? He told me it was common on Pacificas. I could find no reference to this here.
Thanks for the help !