got this weird whining noise, only when my foot is on the gas pedal, cant really notice it in first gear, but all the others as i accelerate there is a whining noise, sounds like its the diff, but if i let off the pedal, the sound goes away, and if i roll in neutral and rev it up to the rev's my car would be at in gear there is no noise as well, also in neutral rolling down a hill there is no whine either, is my diff going bad or something else to do with the drivetrain?